- amino acid dissociative ionization ionization cross-section optical potential амiнокислота оптичний потенцiал перерiз iонiзацiї Ramsauer–Townsend minimum asymmetry chalcogens critical minimum differential and total cross-sections differential cross section independent-atom model integral cross section ionic fragment ionic fragments ionization ionization potential iнтегральний перерiз iон-фрагмент mass spectrometry method mass spectrum molecular orbital optical spectroscopy method optical theorem partial cross section partial phase shift phase shift