Photoionization Study of L-Valine in the Gas Phase by Vacuum Ultraviolet Synchrotron Radiation

Abstract

The photoionization and photodissociation of L-valine are studied by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry at the photon energy of 13 eV. The ionization energy of L-valine and the appearance energies of major fragments are measured by the photoionization efficiency spectrum in the photon energy range of 8–11 eV. Possible formation pathways of the major fragments, NH2CHC(OH)2+ ( m/z = 75), NH2(CH3)2(CH)2+ ( m/z = 72) and NH2CHCO+ ( m/z = 57), are discussed in detail with the theoretical calculations at the B3LYP/6-31++G (d, p) level. Hydrogen migration is considered as the key way for the formation of NH2CHC(OH)2+ ( m/z = 75) and NH2CHCO+ ( m/z = 57). Further more, other fragments, NH2CHCOOH+ ( m/z = 74), (C H3)2(C H)2+ ( m/z = 56), C4H7+ ( m/z = 55), NH2CHOH+ ( m/z = 46), NH2CH2+ ( m/z = 30) and m/z = 18, species are also briefly described.