Photoionization study of L-valine in the gas phase by vacuum ultraviolet synchrotron radiation

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). Furthermore, other fragments, NH2CHCOOH+(m/z= 74), (CH3)(2)(CH)(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.