The interaction of Na atoms with the molecular surfaces H₂O and CH₃OH: the role of delocalized Na3s electrons
The interaction of Na atoms with H₂O and CH₃OH films is studied with metastable impact electron spectroscopy (MIES) under UHV conditions. The films were grown at 90 (+/ – 10) K on tungsten substrates, and exposed to Na. Na – induced water dissociation takes place whereby OH and CH₃O – species are fo...
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Науковий фізико-технологічний центр МОН та НАН України
2003
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| Zitieren: | The interaction of Na atoms with the molecular surfaces H₂O and CH₃OH: the role of delocalized Na3s electrons / A. Borodin, O. Hofft, U. Kahnert, V. Kempter, A. Allouche // Физическая инженерия поверхности. — 2003. — Т. 1, № 2. — С. 146–154. — Бібліогр.: 23 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860237515620876288 |
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| author | Borodin, A. Hofft, O. Kahnert, U. Kempter, V. Allouche, A. |
| author_facet | Borodin, A. Hofft, O. Kahnert, U. Kempter, V. Allouche, A. |
| citation_txt | The interaction of Na atoms with the molecular surfaces H₂O and CH₃OH: the role of delocalized Na3s electrons / A. Borodin, O. Hofft, U. Kahnert, V. Kempter, A. Allouche // Физическая инженерия поверхности. — 2003. — Т. 1, № 2. — С. 146–154. — Бібліогр.: 23 назв. — англ. |
| collection | DSpace DC |
| container_title | Физическая инженерия поверхности |
| description | The interaction of Na atoms with H₂O and CH₃OH films is studied with metastable impact electron spectroscopy (MIES) under UHV conditions. The films were grown at 90 (+/ – 10) K on tungsten substrates, and exposed to Na. Na – induced water dissociation takes place whereby OH and CH₃O – species are formed, and Na – atoms
become ionized. At small Na exposures the outermost solvent layer remains largely intact as concluded from
the absence of MIES signals caused by the reaction products. However, emission from OH and CH₃O – species, located at the film surface, occurs at larger exposures. In the same exposure range also emission from Na3s – ionization can be detected. The corresponding spectral structure occurs at an energetic position different from that found on metals or semiconductors. For the (Na – water) system the results are compared with First – Principles calculations on (Na)₂(H₂O)₁₀ clusters concerned with the electron and proton exchange within the cluster. Experiment and theory agree in the energetic positions of the main spectral features from water and
sodium ionization. The calculations suggest that the 3sNa emission observed experimentally is due to the ejection of solvated 3s electrons which are trapped between the Na – core and water molecules of the surrounding water shell. The simultaneous emergence of dissociation products, OH and CH₃O, and solvated 3s electrons suggests that the delocalization and, consequently, the solvation plays an important role in the Na – water (methanol) reaction. Keywords: metastable impact electron spectroscopy (MIES), water, methanol, ice, solvation, alkali.
Взаємодія атомів Na із плівками H₂O та CH₃OH вивчалася методом електронної спектроскопії метаста
більних зіткнень (ЕСМЗ) в умовах надвисокого вакууму. Плівки були вирощені при температурі 90
(+/ –10) K на вольфрамових підкладинках і піддавалися впливу Na. Індукована Na дисоціація води відбувалася при формуванні груп ОН і CH₃O та іонізації атомів Na. За малих експозицій Na, найбільш віддалений розчинний шар залишається, в значній мірі, неушкодженим, що випливає з відсутності сигналів ЕСМЗ, зумовлених продуктами реакції. Однак, за великих часів експозиції спостерігається випро
мінювання від груп ОН та CH₃O, які локалізовані на поверхні плівки. У цьому ж діапазоні експозиції може бути визначена емісія, яка позв’язана з наявністю Na3s іонізації. Відповідний спектральний склад харак
терний для енергетичних спектрів відмінних від знайдених для металів і напівпровідників. Для системи (Na–вода) результати порівнюються з розрахунками для кластерів (Na)₂(H₂O)₁₀, з урахуванням електронної і протонної взаємодії усередині кластера. Експеримент і теорія збігаються за основними спектраль
ними характеристиками енергетичних спектрів від води та іонізованого натрію. Розрахунки підтверд-
жують, що 3sNa емісія, яка спостерігається експериментально пов’язана із випущенням розчинених 3s електронів, що локалізовані між ядром Na та молекулами води навколишньої водяної оболонки. Одночасне виділення продуктів дисоціації, ОН і CH₃O, та розчинених 3s електронів підтверджує, що делокалізація і, відповідно, розчинення відіграють важливу роль у реакціях Na–вода (метанол).
Взаимодействие атомов Na с пленками H₂O и CH₃OH изучалось методом электронной спектроскопии метас
табильных соударений (ЭСМС) в условиях сверхвысокого вакуума. Пленки были выращены при
температуре 90 (+/ –10) К на вольфрамовых подложках и подвергались воздействию Na. Индуцированная Na диссоциация воды происходила при формировании групп ОН и CH₃O и ионизации атомов Na. При малых экспозициях Na наиболее удаленный растворенный слой остается в значительной степени неповрежденным, что следует из отсутствия сигналов ЭСМС, обусловленных продуктами реакции. Однако, при больших временах экспозициии наблюдается излучение от групп ОН и CH₃O локализованных на поверхности пленки. В этом же диапазоне экспозиции может быть определена эмиссия, связанная с наличием Na3s ионизации. Соответствующий спектральный состав характерен для энергетических спектров отличных от найденных для металлов и полупроводников. Для системы (Na–вода) результаты сравниваются с расчетами для кластеров (Na)₂
(H2
O)₁₀, с учетом электронных и протонных взаимодействий внутри кластера. Эксперимент и теория совпадают по основным спектральным характеристикам энергетических спектров от воды и ионизированного натрия. Расчеты подтверждают, что 3sNa эмиссия, наблюдаемая экспериментально, связана с испусканием растворенных 3s электронов, локализованных между ядром Na и молекулами воды окружающей водной оболочки. Одновременное выделение продуктов диссоциации, ОН и CH₃O, и растворенных 3s электронов подтверждает, что делокализация и, соответственно, растворение играют важную роль в реакциях Na–вода (метанол).
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| fulltext |
146 ФІП ФИП PSE, 2003, том 1, № 2, vol. 1, No. 2
INTRODUCTION
The chemistry on molecular films, water in
particular, is a challenging field for surface science
because of the complexity of the three – dimensional
system under study: in the mobile molecular
environment the balance between solvation, chemi-
cal reactions, stabilization of the solute and the
reaction products are important factors. Although the
reaction of Na atoms with water, yielding NaOH
and H2, is a well – known exothermic reaction, the
underlying mechanism for this simple – looking
process is not well understood. One particular reason
is that it is not easy to obtain direct detailed infor-
mation on the 3sNa electron which plays an active
role in this process. In order to overcome this prob
lem we have started to study the interaction of Na
with films of amorphous solid water (SW) by com-
bining the Metastable Impact Electron Spectroscopy
(MIES) and Ultra-violet photoemission spectroscopy
(UPS) [1, 2, 3, 4]. As compared to UPS, MIES pos-
sesses a rather large sensitivity for the detection of
the 3sNa electron, and its pronounced surface sen-
sitivity allows, in combination with UPS, to dis-
tinguish between species adsorbed atop and under-
neath the surface under study. So far, the main fin-
dings are that Na – induced water dissociation is
certainly efficient above 110K, and that the 3sNa
electron is involved in the dissociation reaction. As
compared to Na adsorption on solid surfaces, metals
and semiconductors in particular, a peculiar shift of
the Na3s –structure is seen in the MIES spectra [3,
4], namely for adsorption on water the 3s – ionization
energy is smaller by 1eV. A quali-tative explanation
for the lowering of the 3s – ioni-zation energy has
been attempted [4] using Born’s model in which Na
is thought to be surrounded, at least partially, by
water molecules; this situation is modeled by
embedding the Na in a cage formed by the
surrounding dielectric medium.
Theory has studied the Na – water interaction by
applying First – Principles and/or Molecular Dyna-
mics methods to Na – water clusters [5, 6, 7, 8]. This
work shows that the 3s – electron becomes delo-
calized from its respective core and is trapped bet-
ween Na and the protons of the shell of hydrating
water molecules pointing towards the Na. The elect-
ron distribution is unique in the sense that the
electron becomes trapped by the surrounding (O –
H) – bonds, and has no positive charge near the center
of the charge distribution. It was demonstrated that
the solvated 3s – electron plays an important role
for the dissociation of the water [8]. In this last paper,
PACS: 34.50.Dy, 68.47.–b, 79.60.Dp, 82.30
THE INTERACTION OF Na ATOMS WITH THE MOLECULAR SURFACES H2 O AND
CH3OH: THE ROLE OF DELOCALIZED Na3s ELECTRONS
A. Borodin*,**, O. Hцfft*, U. Kahnert*, V. Kempter*, A. Allouche***
*Institut fь r Physik und Physikalische Technologien,
Technische Universitдt Clausthal, (Clausthal – Zellerfeld)
Germany
**Institute for High Technologies, V.N. Karazin Kharkiv National University
Ukraine
***Physique des Interactions Ioniques et Molйculaires, (Marseille Cedex 20)
France
Reseived 02.07.2003
The interaction of Na atoms with H2O and CH3OH films is studied with metastable impact electron spectroscopy
(MIES) under UHV conditions. The films were grown at 90 (+/ – 10) K on tungsten substrates, and exposed to
Na. Na – induced water dissociation takes place whereby OH and CH3O – species are formed, and Na – atoms
become ionized. At small Na exposures the outermost solvent layer remains largely intact as concluded from
the absence of MIES signals caused by the reaction products. However, emission from OH and CH3O – species,
located at the film surface, occurs at larger exposures. In the same exposure range also emission from Na3s –
ionization can be detected. The corresponding spectral structure occurs at an energetic position different from
that found on metals or semiconductors. For the (Na – water) system the results are compared with First –
Principles calculations on (Na)2(H2O)10 clusters concerned with the electron and proton exchange within the
cluster. Experiment and theory agree in the energetic positions of the main spectral features from water and
sodium ionization. The calculations suggest that the 3sNa emission observed experimentally is due to the
ejection of solvated 3s electrons which are trapped between the Na – core and water molecules of the surrounding
water shell. The simultaneous emergence of dissociation products, OH and CH3O, and solvated 3s electrons
suggests that the delocalization and, consequently, the solvation plays an important role in the Na – water
(methanol) reaction. Keywords: metastable impact electron spectroscopy (MIES), water, methanol, ice, solvation,
alkali.
147ФІП ФИП PSE, 2003, том 1, № 2, vol. 1, No. 2
First – Principles calculations were carried out on
clusters consisting of one or two Na atoms and their
water environment with the goal to shed light into
the mechanisms for exchange of electrons and pro-
tons between the constituents of the cluster. In par-
ticular, the 3s molecular orbital energy becomes 0,9
eV smaller after hydration.
The new detailed MIES data reported in the
present paper were collected with the purpose to
make a detailed comparison with the predictions of
Ref.[8]. This required the extraction of density
functional theory (DFT) density of states (DOS) in-
formation from Ref.[8]; this information, before and
after the transfer of the delocalized electron to the
protons of the surrounding water has taken place, is
compared with the MIES spectra. In addition, we
present MIES data for the interaction of Na with
methanol in order to check the predictions of theory
concerning the mechanism for the Na – CH3OH
reaction.
EXPERIMENTAL REMARKS
The experiments, described in detail elsewhere [9,
10], were carried out under ultra high vacuum (UHV)
conditions (base pressure < 2×10–10 Torr). AES and
XPS are used to characterize the chemical compo-
sition of the tungsten substrate employed for the
deposition of the molecular films. With LEED it was
checked that the molecular films are amorphous. The
electronic structure of the molecular films was
studied by applying MIES and UPS(HeI and II). In
MIES metastable helium atoms (23S/21S) eject
electrons from the edge of the surface under study.
The application of MIES to surface spectroscopy is
well documented [11, 12]. If the Na adsorbate is not
fully ionized, a spectral feature is expected from the
presence of 3s – charge density at the Na core. With
UPS (HeI) the partially occupied 3s – orbital is prac-
tically not seen due to its low photoionization cross
section [13]. However, in MIES it causes a prominent
feature, Na(3s), close to EF which is clearly seen on
metals and semiconductors for coverages larger than
about 0,5ML [11, 12]. This underlines the power of
MIES for investigating the chemistry between Na
and water, which is driven by the 3s – valence elect-
ron. For the study of the Na – induced changes in
the electronic structure of the molecular films we
have confined ourselves to MIES because the UPS
(HeI and II) spectra give no information on the 3sNa
electron.
The primary result of the experiments are electron
energy spectra versus the kinetic energy of the
emitted electrons. By choosing a suitable bias voltage
between the target and the electron energy analyzer,
the energy scales in the figures are adjusted in such
a way that electrons emitted from the Fermi level,
denoted by EF, i.e. electrons with the maximal kinetic
energy, appear at 19.8eV (which is the potential
energy of the metastable He atoms employed for
MIES). With this particular choice of the bias vol-
tage, the low – energy cutoff in the spectra gives
directly the surface work function (WF), irrespective
of the actual interaction process which produces the
electrons. For a convenient comparison with theory
we present our data as a function of the binding ene-
rgy of the emitted electrons prior to their ejection.
Electrons emitted from the Fermi level, i.e. those
with the 19,8 eV kinetic energy, appear at binding
energy EB = 0 eV with respect to the Fermi level.
Na atoms were dosed employing carefully out-
gassed commercial dispenser sources (SAES Get-
ters). They operate at a rate of 0.05 ML/min, typi-
cally. The procedure for the calibration of the alkali
coverage is described elsewhere [14]. The exposure
is given in units of monolayer equivalents (MLE);
at 1MLE the surface would be covered by one Na
monolayer if penetration of the Na into the molecular
films could be neglected.
The surface temperature can be varied between
about 90 and 700 K; at present the accuracy of the
temperature calibration is 10 K. The surface was
exposed to water by backfilling the chamber at a
substrate temperature between 110 and 130K. This
ensures the formation of a closed, non – porous and
amorphous SW film [15]. The formation of an orde-
red film would require a certain degree of mobility
of the water molecules; below 140K this mobility
does not exist anymore. The relative amount of sur-
face – adsorbed water can be estimated on the basis
of earlier work with themal desorbtion spectroscopy
(TPD) and MIES [1, 10]. Prior to Na exposure the
surface prepared as described above was cooled to
the desired temperature.
COMPUTATIONAL DETAILS
The method of computation was fully exposed in
[8]. A Density Functional Theory (DFT) calculation
was carried out at the B3LYP/6 – 31+g (d, p) level
of approximation. This was performed on several
cluster models in order to investigate the potential
energy surfaces associated to neutral sodium hyd-
rolysis.
The first model included only one sodium atom
in a cluster consisting of seven water molecules.
The calculated barrier of activation was equal to
31,6 kJ⋅mol–1 after correction of the zero point
energy. The two others clusters involved two atoms
embedded into clusters of seven and ten water
A. BORODIN, O. HЦFFT, U. KAHNERT, V. KEMPTER, A. ALLOUCHE
148 ФІП ФИП PSE, 2003, том 1, № 2, vol. 1, No. 2
THE INTERACTION OF Na ATOMS WITH THE MOLECULAR SURFACES H2 O AND CH3OH: THE ROLE OF DELOCALIZED...
molecules, respectively. The associated barriers of
activation were 37,2 and 33,2 kJ⋅mol–1, respectively,
i.e. the barriers decrease with the number of hydra-
ting molecules.
The calculation of the free activation energies
shows that at low temperature the two Na mechanism
is more easy. However, all the investigated models
involve the 3sNa electron solvation, and are strongly
dependent of the electrostatic fields generated by the
water cluster.
It was established previously that the interaction
of He* with clean and Na covered water films is via
the Auger deexcitation process. This implies that the
MIES spectra image the surface density of states
(SDOS) directly [11, 12]. The SDOS, needed for the
comparison with the MIES spectra, have been
obtained by dressing the DFT molecular energy level
distributions with Lorentzian functions of arbitrary
height and an half width of 0,25 eV.
RESULTS
The following spectral features are expected when
Na and water interact with surfaces [1, 2, 3, 4]: the
2pNa-orbital, due to its high ionization energy, is
not accessible by the chosen techniques. If the Na
adsorbate is not fully ionized, a spectral feature is
expected from the presence of 3s – charge density at
the Na core. It causes a prominent feature, Na(3s),
close to EF which is clearly seen on metals and
semiconductors for coverages larger than about
0,5ML [11, 12].
Molecularly adsorbed water produces three
peaks, both in MIES and UPS, identified as emission
from the three uppermost occupied water orbitals
1b1, 3a1, and 1b2 [16, 17] (binding energies 7,8; 10,0
and 13,2 eV, respectively). In contrast, the adsorption
of water onto partially alkalated titania leads to water
dissociation provided the precoverage is larger than
about 0,5 monolayers [10]. The ionization of the OH
1π and the 3σ orbitals yields peaks at EB= 7,0 and
11,2 eV, respectively [16, 17]. On metal substrates
the Na – H2O interaction can lead to complete
dissociation of H2O. In this case atomic oxygen
species, stabilized by Na+ ions, will be seen. As a
particular example, the ionization of O2– species will
give rise to a single peak around EB =3,6 eV [18].
Fig. 1 (upper set of spectra) presents the MIES
results obtained during Na deposition on a water film
(3 bilayers of water) held at 90K. For pure water we
see indeed the structures 1b1, 3a1, and 1b2 from the
ionization of the three highest occupied water MO’s
(top spectrum). Under Na exposure the spectra
remain unchanged initially except for a change of
the peak positions simultaneously with the observed
Na – induced WF decrease (1 eV), and a smearing –
out of the water features 1b1, 3a1, and 1b2.
Above 0,5MLE a shoulder emerges at the
position where emission from 1π of OH is expected
[16, 17]. Accordingly, we have denoted the shoulder
by 1π. The contribution expected from the ionization
of 3σ of OH at a binding energy larger by 3,7 eV
[16, 17] is obscured by the emission from 3a1. In the
same exposure range emission, labeled Na (3s),
appears. It resembles closely to the Na – induced
emission seen with metals and semiconductors for
coverages larger than about 0,5 ML. In these cases,
the emission is due to the presence of s – charge
density at the alkali core, i.e. the Na adsorbate is not
fully ionized anymore. We assume that Na (3s) has
the same origin. However, the emission is peaked at
EB = 2,3 eV which is about 1 eV larger than on solid
surfaces. This binding energy is with respect to EF.
As determined from the onset of the MIES spectra
at low kinetic energies, the work function (WF) is
2eV, and thus EB is located 2eV below the vacuum
level. Thus, under the present conditions the 3s –
ionization energy is (EB + WF)eV = 4,3 eV. Although
no Na signature is seen in the early stage of exposure,
Na species must become adsorbed/incorporated into
the water film as suggested by the decrease of WF
and the concomitant shift of the water spectra. Since
no 3s – emission is seen, we conclude that no 3s
electrons are present at the film surface.
Compared to 130 K [3, 4], Na(3s) appears already
at lower exposures, and, thus, Na penetration into
the water film is less likely. In addition, other than
at 130 K, H2O and OH features appear simultaneous-
ly over the entire studied range of exposures, indica-
ting that the (Na – water) reaction is blocked before
the entire film surface is converted into NaOH comp-
lexes. The present results are rather similar to the
10 K results [3] where little reaction was seen, and
the Na species stayed at the surface.
The surface prepared by Na exposure was heated
stepwise between 90 and 650 K. The results (lower
set of spectra in fig. 1) support the interpretation
given to the feature 1π: the molecular water desorbs
at 155 K while OH – species can be detected on the
surface up to 390 K as suggested by the presence of
the two peaks 1π and the 3σ at a distance of 3,7 eV
at positions that agree well with [16, 17]. The 1π
shoulder develops smoothly into the peak labeled
1π, suggesting that 1π, seen before the water desorp-
tion, is indicative for OH – species from the reaction
of Na with water molecules.
When annealing further, the OH – features
disappear at 390 K. Apart from the tungsten substrate
emission, seen between about 5 and 13 eV, a promi-
149ФІП ФИП PSE, 2003, том 1, № 2, vol. 1, No. 2
nent peak appears at 4 eV; it persists up to 600 K.
This finding is consistent with OH – decomposition
whereby atomic oxygen remains at the surface. The
energetic position is characteristic for O2– species,
stabilized by Na ions.
Na disappears from the surface when heating
from 90 to 110 K, presumably because the mobility
of the water molecules increases which leads to the
solvation of Na in the film.
Fig. 1. MIES spectra for the adsorption of Na on solid water (3 layers) prepared on tungsten (90K) (upper set of spectra), and the
spectral changes resulting from annealing the Na/H2O system over the indicated temperature range (lower set of spectra) (see text
for the acronyms employed in the figure).
A. BORODIN, O. HЦFFT, U. KAHNERT, V. KEMPTER, A. ALLOUCHE
150 ФІП ФИП PSE, 2003, том 1, № 2, vol. 1, No. 2
THE INTERACTION OF Nа ATOMS WITH THE MOLECULAR SURFACES H2 O AND CH3OH: THE ROLE OF DELOCALIZED...
Fig. 2 presents MIES results for CH3OH, obtained
in the same manner as described above (fig.1) for
water. The tungsten substrate is held at 90 K during
the film preparation. The top spectrum is for the
methanol film (4 layers thick) prior to Na exposure.
The upper set of spectra is obtained during the Na
exposure of the film. According to Refs.[2, 19, 20],
M1 to M5 have nO⊥, nOII, σCO; πCO , and σOH character,
respectively. As a consequence of the exposure to
Na M1 to M5 shift to larger EB’s, simultaneously
Fig. 2. MIES spectra for the Na – exposed film of solid CH3OH (4 layers prepared on tungsten (90K) (upper set of spectra), and
the spectral changes resulting from annealing the Na/CH3OH system over the indicated temperature range (lower set of spectra)
(see text for the acronyms employed in the figure).
151ФІП ФИП PSE, 2003, том 1, № 2, vol. 1, No. 2
with the observed decrease of WF by 1,3 eV. In
addition, the structure, labeled πCH3
, develops. In
studies which concentrate on the electronic structure
of CH3OH – ice, we established that πCH3
together
with (σCO; nO), overlapping with M3;4, must be
attributed to methoxy, CH3O, species from the dehyd-
rogenation of CH3OH by Na [21]: the structures πCH3and (σCO; nO), separated by about 5 eV, result from
the ionization of the antibonding π – MO’s, located
at the CH3 – group and the oxygen core (πCH3 and
nO), and from the σ – MO along the (C – O) – direc-
tion. Support for this identification comes from the
study of the oxygenation of CH3OH on a oxygen
precovered Cu (111) surface [22]. The structure Na
(3s) at EB = 2 eV develops as a consequence of the
Na – exposure, and can clearly be noticed above 0,4
MLE; the WF of the Na – exposed film saturates
after a WF decrease of 1 eV.
The lower set of spectra in fig. 2 was obtained
when heating from 90 to 650 K. M1 to M5 from
CH3OH disappear when annealing to 165 K while
the structures attributed to CH3O, in particular πCH3
,
persist up to 460K. We attribute the emission seen
between 5 and 13 eV at higher temperatures to the
tungsten substrate. During annealing Na (3s) behaves
similar as for water, shifts to smaller EB‘s and di-
sappears at 110 K. In auxiliary experiments on films
prepared at 120K we have established that there is
no Na desorption at these temperatures; instead Na
penetrates into the CH3OH film.
DISCUSSION
A qualitative explanation of the observed lowering
of the 3s Na ionization energy in aqueous
environment has been attempted [4] using Born’s
model, applied previously to explain photoelectron
spectra from liquid water [23]: the Na atom is thought
to be surrounded, at least partially, by water mole-
cules. In Born’s model this situation is modeled by
embedding the Na in a cage formed by the surroun-
ding dielectric medium. This leads to a decrease of
the 3s– ionization energy by δW = 1/8πε0r0⋅(1– 1/ε),
where r0 is the cage radius (about 0,2 nm for water
[23]) and ε the dielectric constant of water. Using ε
= 1,5 [23], one obtains an 1eV reduction of the 3s –
ionization energy for the embedded Na atom, in
reasonable agreement with experiment [4]. Of cour-
se, this naive model gives no hint how to explain the
observed Na – induced water dissociation.
The sodium interaction with water ice will now
be discussed on the basis of the theory results for
sodium hydroxyl formation in water clusters [8]. The
key point was to consider the consequences of the
hydrolysis of a single Na atom as well as of Na2 di-
mers interacting with water clusters. The role of 3s
Na electrons solvated by three surrounding water
molecules was studied. As a consequence, the 3s –
electrons are located very far from their original nuc-
lei. The fundamental role of the electric field gene-
rated by the metal atoms inside the water cluster was
also pointed out. A major effect of the Na trapping
is the strong perturbation of the molecular energy
levels distribution, narrowing the DOS bands. The
following considerations go beyond ref. [8] in as
much as a DOS, suitable for comparison with the
MIES spectra, has been generated from the energy
levels of the sodium – water clusters considered in
ref.[8].
As pointed out in section 3, significant Na(3s)
and 1π emission (attributed to the reaction product
OH) is not seen below 0,5 MLE. This could be in-
dication that this minimum Na concentration is requi-
red for the water dissociation to occur. Indeed, the
First – Principles calculations carried out on clusters
consisting of one and two Na atoms and their water
environment [5, 6, 7, 8] suggest that the presence of
Na dimers (or even trimers [6]) faci-litates the water
dissociation.
We show now that the MIES spectra and the DFT
results for the DOS for two sodium atoms trapped
in a (H2O)10 cluster before and after Na2 hydrolysis
are consistent (Fig. 3). As suggested by the results
of section 4, we suppose in the following that un-
reacted, but solvated Na – species (prior to the reac-
tion) and OH – species from the Na – induced hyd-
rolysis are both present at the surface. The DFT –
DOS before Na – ionization shows 4 peaks in the 0
to 20 eV window labeled A, B, C and D as in ref.[8].
Peak A corresponds to the solvated electron (denoted
by Na (3s) in the MIES spectra). Peaks B and C cor-
respond mainly to the π and σ water lone pairs of
electrons involved in OH bonds (denoted 1b1 and 3a1
in MIES). Peak D (labeled 1b2 in MIES) is the
antisymmetric OH contribution. B is well reflected
in the experimental spectrum. C is also seen in the
MIES spectrum, but overlaps with the contribution
of the “ionized” system, consisting of Na+, the sol-
vated electron and the water cluster, since as men-
tioned before, the MIES DOS is a superposition of
“ionized” and “non – ionized” (before the transfer
of the solvated electron to nearby protons takes place)
species. D is also present in the experimental DOS,
but merely as a shoulder.
After hydrolysis, the solvated electron signal
disappears from the DFT – DOS. Two shoulders
appear in the DFT – DOS corresponding to the shift
of the two water LP’s combined to the two hydroxyl
groups issued from Na2 ionization; a larger cluster
A. BORODIN, O. HЦFFT, U. KAHNERT, V. KEMPTER, A. ALLOUCHE
152 ФІП ФИП PSE, 2003, том 1, № 2, vol. 1, No. 2
THE INTERACTION OF Na ATOMS WITH THE MOLECULAR SURFACES H2 O AND CH3OH: THE ROLE OF DELOCALIZED...
would have produced a broad band analogous to the
shoulder in the MIES pattern in the same energy
region. The former peaks B, C and D are shifted
towards the Fermi level, and the overall combination
is well reflected in the experimental curve. The σ
hydroxyl OH, located around 25 eV, is not displayed
in this figure.
From the present experiment it is not possible to
determine unambiguously whether the active Na
species are single atoms, dimers (as assumed in the
present work) or, as proposed in ref. [6], as trimers.
Nevertheless, the comparison between theory and
experiment appears to be meaningful enough to
support the reaction pathway involving Na dimers:
in the first step, after film adsorption, Na is trapped
inside the cluster. This perturbs strongly the original
water DOS in mixing more intimately the lone pair
and antisymmetric water OH wave functions.
Therefore, the proton tunneling from one water
molecule to a neighbouring one is greatly facilitated.
The acceptor molecule releases one of its own
protons to another neighbour. This process continues
from site to site until the end of the H – bonded chain
is reached. This happens at the protons pointing to-
Fig. 3. DOS of the Na2(H2O)10 – cluster defined in the text and comparison with the results of fig.1 (heavy spectrum).
153ФІП ФИП PSE, 2003, том 1, № 2, vol. 1, No. 2
ward the solvated electrons. Such a proton is therefore
able to capture one of these electrons producing, in
the first step, an H radical atom, and then a H2 mo-
lecule.
When heating beyond 115K Na species disappear
from the surface, becoming solvated in the water film.
Therefore, a comparison of MIES results and theory
is limited to temperatures below 115 K.
A few comments are in order concerning the
mechanism for the interaction of Na with methanol.
The experiment demonstrates that, as for water, delo-
calization of the 3s – electron takes place, and plays
an important role in producing H radical atoms by
dehydrogenation of methanol as documented by the
formation of CH3O species. In analogy to water, we
expect that the 3s – electron is trapped between the
Na – core and protons of the OH – group of CH3OH
molecules surrounding the Na+ core. A possible reac-
tion path that resembles that of the single Na case
discussed in Ref. [8] for the reaction of Na with water,
is as follows: the delocalized electron is transferred
to one of the protons of the methanol molecules sur-
rounding the Na species. The particular proton that
captured the solvated electron is released from its
molecule, and leaves CH3O
– species behind. The Na+
core and the CH3O
– species form (Na+ CH3O
–) –
complexes. This is in agreement with MIES which
simultaneously detects 3sNa, CH3OH (prior to the
reaction), and CH3O– species (after the reaction) at
the surface.
CONCLUSIONS
The present study, employing the Metastable Impact
Electron Spectroscopy (MIES), gives insight into the
chemistry between Na and water (methanol) ice films
held at 80 K. It concentrates on the role of the Na3s
electron for the reaction between Na and the mole-
cular films. For water the interaction leads to OH –
formation which, at 80 K, appears to be confined to
the film surface mainly. This is in contrast with
previous results at 130 K film temperature where the
reaction involves the entire film. For methanol the
reaction products are identified as CH3O – species.
As for water, at 80 K the reaction is mainly confined
to the film surface. For water the MIES spectra are
in good agreement with the density of the states in
Na2(H2O)10 clusters as obtained from First –
Principles DFT calculations. In particular, theory and
experiment agree well in the energetic position of
the 3s electron. Theory predicts that the 3s electron
is delocalized from its Na+ core, and is trapped
between the core and surrounding solvent molecules.
It is therefore suggested that in both cases, water and
methanol, the 3sNa electrons are solvated in the
A. BORODIN, O. HЦFFT, U. KAHNERT, V. KEMPTER, A. ALLOUCHE
respective molecular surroundings. Calcul-ations
and experiment both underline that the delocalized
electron triggers the Na – water reaction leading to
the formation of NaOH.
On the basis of the available theory results for
the Na – water system and the comparison of the
experimental results for Na – water and – methanol
we propose a scenario for the Na – methanol reac-
tion. As for water, it is initiated by delocalized 3sNa
electrons which become transferred to one of the
protons of surrounding CH3OH molecules leading
to its dehydrogenation.
ACKNOWLEDGEMENTS
The Marseille – Clausthal cooperation was
supported by the COST 19 action of the EU.
REFERENCES
1. Gьnster J., Krischok S., Stultz J., Goodman D.W.
Interaction of Na with Multilayer Water on
MgO(100)//J. Phys. Chem. B – 2000, 104, 7977.
2. Gьnster. J., Krischok S., Kempter V., Stultz J., Good-
man D.W. Characterization of coadsorbed mole-
cular species in a multilayer solvent environ-ment
on insulating surfaces//Surf. Rev. Lett.– 2002.–T. 9.–
P. 1511.
3. Krischok S., Hцfft O., Gьnster J., Souda R., Kemp-
ter V. The chemistry of alkali atoms on solid water:
Study with MIES and UPS// NIM B– 2003.– T. 203.–
P. 124.
4. Krischok S., Hцfft O., Kempter V.Interaction of
alkali atoms with water multilayers adsorbed on
TiO2(110): A study with MIES and UPS//Surf. Sci.
– 2003. – № 532 – 535. – P. 370.
5. Barnett R.N., Landman U. Hydration of sodium in
water clusters // Phys. Rev. Lett. – 1993. – T. 70. –
P. 1775.
6. Mundy C.J., Hutter J., Parinello M. Microsolva-
tion and Chemical Reactivity of Sodium and Water
Clusters// J. Am. Chem. Soc. – 2000. – T. 122. –
P. 4873.
7. Tsurusawa T., Iwata S. Electron-hydrogen bonds and
OH harmonic frequency shifts in water cluster
complexes with a group 1 metal atom, M(H2O)n
(M=Li and Na)//J. Chem. Phys.– 2000. – T. 112.–
P. 5705.
8. Ferro Y., Allouche A. Sodium hydroxide formation
in water clusters: The role of hydrated electrons and
the in uence of electric fields//J. Chem. Phys. –
2003.– T. 118. – P. 10461.
9. Stracke P., Krischok S., Kempter V. Ag-adsorption
on MgO: investigations with MIES and UPS// Surf.
Sci. – 2001. – T. 473. – P. 86.
10. Krischok S., Hцfft O., Gьnster J., Stultz J., Good-
man D.W., KempterV. H2O interaction with bare and
Li-precovered TiO2: Studies with electron spectro-
scopies (MIES and UPS(HeI and II))//Surf. Sci. –
2001. – № 495. – P. 211.
11. Harada Y., Masuda S., Osaki H. Electron Spectro-
scopy Using Metastable Atoms as Probes for Solid
Surfaces//Chem. Rev. – 1997. T. 97. – P. 1897.
154 ФІП ФИП PSE, 2003, том 1, № 2, vol. 1, No. 2
ВЗАИМОДЕЙСТВИЕ АТОМОВ Na
С МОЛЕКУЛЯРНЫМИ ПОВЕРХНОСТЯМИ
H2O И CH3OH: РОЛЬ ДЕЛОКАЛИЗОВАННЫХ
Na3s ЭЛЕКТРОНОВ
А. Бородин, О. Хоффт, У. Канерт,
В. Кемптер, А. Аллуш
Взаимодействие атомов Na с пленками H2O и CH3OH
изучалось методом электронной спектроскопии метас-
табильных соударений (ЭСМС) в условиях сверх-
высокого вакуума. Пленки были выращены при
температуре 90 (+/ –10) К на вольфрамовых подлож-
ках и подвергались воздействию Na. Индуцированная
Na диссоциация воды происходила при формировании
групп ОН и CH3O и ионизации атомов Na. При малых
экспозициях Na наиболее удаленный растворенный
слой остается в значительной степени неповрежден-
ным, что следует из отсутствия сигналов ЭСМС, обу-
словленных продуктами реакции. Однако, при боль-
ших временах экспозициии наблюдается излучение
от групп ОН и CH3O локализованных на поверхности
пленки. В этом же диапазоне экспозиции может быть
определена эмиссия, связанная с наличием Na3s иони-
зации. Соответствующий спектральный состав харак-
терен для энергетических спектров отличных от най-
денных для металлов и полупроводников. Для
системы (Na–вода) результаты сравниваются с рас-
четами для кластеров (Na)2(H2O)10, с учетом элект-
ронных и протонных взаимодействий внутри клас-
тера. Эксперимент и теория совпадают по основным
спектральным характеристикам энергетических спек-
тров от воды и ионизированного натрия. Расчеты под-
тверждают, что 3sNa эмиссия, наблюдаемая экспери-
ментально, связана с испусканием растворенных 3s
электронов, локализованных между ядром Na и
молекулами воды окружающей водной оболочки.
Одновременное выделение продуктов диссоциации,
ОН и CH3O, и растворенных 3s электронов подтверж-
дает, что делокализация и, соответственно, растворе-
ние играют важную роль в реакциях Na–вода (мета-
нол).
ВЗАЄМОДІЯ АТОМІВ Na
З МОЛЕКУЛЯРНИМИ ПОВЕРХНЯМИ H2O
І CH3OH: РОЛЬ ДЕЛОКАЛІЗОВАНИХ
Na3s ЕЛЕКТРОНІВ
О. Бородін, О. Хоффт, У. Канерт,
В. Кемптер, А. Аллуш
Взаємодія атомів Na із плівками H2O та CH3OH вив-
чалася методом електронної спектроскопії метаста-
більних зіткнень (ЕСМЗ) в умовах надвисокого
вакууму. Плівки були вирощені при температурі 90
(+/ –10) K на вольфрамових підкладинках і піддава-
лися впливу Na. Індукована Na дисоціація води від-
бувалася при формуванні груп ОН і CH3O та іонізації
атомів Na. За малих експозицій Na, найбільш від-
далений розчинний шар залишається, в значній мірі,
неушкодженим, що випливає з відсутності сигналів
ЕСМЗ, зумовлених продуктами реакції. Однак, за
великих часів експозиції спостерігається випро-
мінювання від груп ОН та CH3O, які локалізовані на
поверхні плівки. У цьому ж діапазоні експозиції може
бути визначена емісія, яка позв’язана з наявністю Na3s
іонізації. Відповідний спектральний склад харак-
терний для енергетичних спектрів відмінних від знай-
дених для металів і напівпровідників. Для системи
(Na–вода) результати порівнюються з розрахунками
для кластерів (Na)2(H2O)10, з урахуванням електрон-
ної і протонної взаємодії усередині кластера. Експе-
римент і теорія збігаються за основними спектраль-
ними характеристиками енергетичних спектрів від
води та іонізованого натрію. Розрахунки підтверд-
жують, що 3sNa емісія, яка спостерігається експери-
ментально пов’язана із випущенням розчинених 3s
електронів, що локалізовані між ядром Na та моле-
кулами води навколишньої водяної оболонки. Одно-
часне виділення продуктів дисоціації, ОН і CH3O, та
розчинених 3s електронів підтверджує, що делока-
лізація і, відповідно, розчинення відіграють важливу
роль у реакціях Na–вода (метанол).
12. Morgner H. The characterisation of liquid and so-lid
surfaces with metastable helium atoms// Adv. At.
Molec. Opt. Phys. – 2000. – T. 42. – P. 387.
13. Price W.C. Electron Spectroscopy: Theory, techni-
ques and applications//Electron Spectroscopy: Theo-
ry, techniques and applications. Vol. 1 (C.R. Brundle,
A.D. Baker, eds., Academic Press, N.Y., 1977)151p.
14. Brause M., Skordas S., Kempter V. Study of the elect-
ronic structure of TiO2(110) and Cs/TiO2(110) with
metastable impact electron spectroscopy and ultra-
violet photoemission spectroscopy (HeI)// Surf. Sci.
– 2000. – № 445.– P. 224.
15. Stevenson K.P., Kimmel G.A., Dohnalek Z., Smith R.S.,
Kay B.D.Controlling the Morphology of Amorphous
Solid Water//Science –1999. T. 283. – P. 1505.
16. Thiel P.A., Madey T.E. The interaction of water with
solid surfaces: Fundamental aspects//Surf. Sci. Rep.
– 1987. – T. 7. – P. 211.
17. Henderson M.A./The interaction of water with solid
surfaces: Fundamental aspects revisited//Surf. Sci.
Rep. – 2002. – № 285. P. 1.
18. Maus–Friedrichs W., Dieckhoff S., Wehrhahn M.,
Pь lm S., Kempter V. The interaction of alkali atoms
with oxygen on W(110) as studied by UPS and meta-
stable impact electron spectroscopy I. Li and Na//
Surf. Sci. – 1992.– № 271. – P. 113.
19. Kimura K. et al. Handbook of HeI Photoelectron
Spectra of Fundamental Organic Molecules// Hand-
book of HeI Photoelectron Spectra of Fundamental
Organic Molecules, Halsted Press, N.Y.
20. Yamakado H., Yamauchi M., Hoshino S., Ohno K.
Penning Ionization of CH3OH, (CH3)2O, and
(CH3CH2)2O by Collision with He(23S) Metastable
Atoms// J. Phys. Chem. – 1995, 99, 17093.
21. Borodin A., Hofft O., Krischok S., Kempter V. Ioniza-
tion and solvation of CsCl interacting with solid water
// J. Phys. Chem. – 2003, 107(35), 9357.
22. Pцllmann S., Bauer A., Ammon C., Steinrьck H.P.
Spring Meeting of the DPG//Spring Meeting of the
DPG, Dresden – 2003, Book of Abstr., P. 378.
23. Faubel M. Photoionization and Photodetachment.
Part I//World Scientific, Singapore, 2000) 634.
THE INTERACTION OF Na ATOMS WITH THE MOLECULAR SURFACES H2 O AND CH3OH: THE ROLE OF DELOCALIZED...
|
| id | nasplib_isofts_kiev_ua-123456789-98433 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1999-8074 |
| language | English |
| last_indexed | 2025-12-07T18:25:41Z |
| publishDate | 2003 |
| publisher | Науковий фізико-технологічний центр МОН та НАН України |
| record_format | dspace |
| spelling | Borodin, A. Hofft, O. Kahnert, U. Kempter, V. Allouche, A. 2016-04-14T15:56:13Z 2016-04-14T15:56:13Z 2003 The interaction of Na atoms with the molecular surfaces H₂O and CH₃OH: the role of delocalized Na3s electrons / A. Borodin, O. Hofft, U. Kahnert, V. Kempter, A. Allouche // Физическая инженерия поверхности. — 2003. — Т. 1, № 2. — С. 146–154. — Бібліогр.: 23 назв. — англ. 1999-8074 PACS: 34.50.Dy, 68.47.–b, 79.60.Dp, 82.30 https://nasplib.isofts.kiev.ua/handle/123456789/98433 The interaction of Na atoms with H₂O and CH₃OH films is studied with metastable impact electron spectroscopy (MIES) under UHV conditions. The films were grown at 90 (+/ – 10) K on tungsten substrates, and exposed to Na. Na – induced water dissociation takes place whereby OH and CH₃O – species are formed, and Na – atoms
 become ionized. At small Na exposures the outermost solvent layer remains largely intact as concluded from
 the absence of MIES signals caused by the reaction products. However, emission from OH and CH₃O – species, located at the film surface, occurs at larger exposures. In the same exposure range also emission from Na3s – ionization can be detected. The corresponding spectral structure occurs at an energetic position different from that found on metals or semiconductors. For the (Na – water) system the results are compared with First – Principles calculations on (Na)₂(H₂O)₁₀ clusters concerned with the electron and proton exchange within the cluster. Experiment and theory agree in the energetic positions of the main spectral features from water and
 sodium ionization. The calculations suggest that the 3sNa emission observed experimentally is due to the ejection of solvated 3s electrons which are trapped between the Na – core and water molecules of the surrounding water shell. The simultaneous emergence of dissociation products, OH and CH₃O, and solvated 3s electrons suggests that the delocalization and, consequently, the solvation plays an important role in the Na – water (methanol) reaction. Keywords: metastable impact electron spectroscopy (MIES), water, methanol, ice, solvation, alkali. Взаємодія атомів Na із плівками H₂O та CH₃OH вивчалася методом електронної спектроскопії метаста
 більних зіткнень (ЕСМЗ) в умовах надвисокого вакууму. Плівки були вирощені при температурі 90
 (+/ –10) K на вольфрамових підкладинках і піддавалися впливу Na. Індукована Na дисоціація води відбувалася при формуванні груп ОН і CH₃O та іонізації атомів Na. За малих експозицій Na, найбільш віддалений розчинний шар залишається, в значній мірі, неушкодженим, що випливає з відсутності сигналів ЕСМЗ, зумовлених продуктами реакції. Однак, за великих часів експозиції спостерігається випро
 мінювання від груп ОН та CH₃O, які локалізовані на поверхні плівки. У цьому ж діапазоні експозиції може бути визначена емісія, яка позв’язана з наявністю Na3s іонізації. Відповідний спектральний склад харак
 терний для енергетичних спектрів відмінних від знайдених для металів і напівпровідників. Для системи (Na–вода) результати порівнюються з розрахунками для кластерів (Na)₂(H₂O)₁₀, з урахуванням електронної і протонної взаємодії усередині кластера. Експеримент і теорія збігаються за основними спектраль
 ними характеристиками енергетичних спектрів від води та іонізованого натрію. Розрахунки підтверд-
 жують, що 3sNa емісія, яка спостерігається експериментально пов’язана із випущенням розчинених 3s електронів, що локалізовані між ядром Na та молекулами води навколишньої водяної оболонки. Одночасне виділення продуктів дисоціації, ОН і CH₃O, та розчинених 3s електронів підтверджує, що делокалізація і, відповідно, розчинення відіграють важливу роль у реакціях Na–вода (метанол). Взаимодействие атомов Na с пленками H₂O и CH₃OH изучалось методом электронной спектроскопии метас
 табильных соударений (ЭСМС) в условиях сверхвысокого вакуума. Пленки были выращены при
 температуре 90 (+/ –10) К на вольфрамовых подложках и подвергались воздействию Na. Индуцированная Na диссоциация воды происходила при формировании групп ОН и CH₃O и ионизации атомов Na. При малых экспозициях Na наиболее удаленный растворенный слой остается в значительной степени неповрежденным, что следует из отсутствия сигналов ЭСМС, обусловленных продуктами реакции. Однако, при больших временах экспозициии наблюдается излучение от групп ОН и CH₃O локализованных на поверхности пленки. В этом же диапазоне экспозиции может быть определена эмиссия, связанная с наличием Na3s ионизации. Соответствующий спектральный состав характерен для энергетических спектров отличных от найденных для металлов и полупроводников. Для системы (Na–вода) результаты сравниваются с расчетами для кластеров (Na)₂
 (H2
 O)₁₀, с учетом электронных и протонных взаимодействий внутри кластера. Эксперимент и теория совпадают по основным спектральным характеристикам энергетических спектров от воды и ионизированного натрия. Расчеты подтверждают, что 3sNa эмиссия, наблюдаемая экспериментально, связана с испусканием растворенных 3s электронов, локализованных между ядром Na и молекулами воды окружающей водной оболочки. Одновременное выделение продуктов диссоциации, ОН и CH₃O, и растворенных 3s электронов подтверждает, что делокализация и, соответственно, растворение играют важную роль в реакциях Na–вода (метанол). The Marseille – Clausthal cooperation was
 supported by the COST 19 action of the EU en Науковий фізико-технологічний центр МОН та НАН України Физическая инженерия поверхности The interaction of Na atoms with the molecular surfaces H₂O and CH₃OH: the role of delocalized Na3s electrons Взаємодія атомів Na з молекулярними поверхнями H₂O і CH₃OH: роль делокалізованих Na3s електронів Взаимодействие атомов Na с молекулярными поверхностями H₂O и CH₃OH: роль делокализованых Na3s электронов Article published earlier |
| spellingShingle | The interaction of Na atoms with the molecular surfaces H₂O and CH₃OH: the role of delocalized Na3s electrons Borodin, A. Hofft, O. Kahnert, U. Kempter, V. Allouche, A. |
| title | The interaction of Na atoms with the molecular surfaces H₂O and CH₃OH: the role of delocalized Na3s electrons |
| title_alt | Взаємодія атомів Na з молекулярними поверхнями H₂O і CH₃OH: роль делокалізованих Na3s електронів Взаимодействие атомов Na с молекулярными поверхностями H₂O и CH₃OH: роль делокализованых Na3s электронов |
| title_full | The interaction of Na atoms with the molecular surfaces H₂O and CH₃OH: the role of delocalized Na3s electrons |
| title_fullStr | The interaction of Na atoms with the molecular surfaces H₂O and CH₃OH: the role of delocalized Na3s electrons |
| title_full_unstemmed | The interaction of Na atoms with the molecular surfaces H₂O and CH₃OH: the role of delocalized Na3s electrons |
| title_short | The interaction of Na atoms with the molecular surfaces H₂O and CH₃OH: the role of delocalized Na3s electrons |
| title_sort | interaction of na atoms with the molecular surfaces h₂o and ch₃oh: the role of delocalized na3s electrons |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/98433 |
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