Ionic dissociation of glycine, alanine, valine and proline as induced by VUV (21.21 eV) photons

Ionic fragmentation of the sublimated α-amino acids glycine, l -alanine, l -proline and l -valine has been studied using a time-of-flight mass spectrometer coupled to a He I lamp (hν = 21.21 eV). Partial ion yields (branching ratios) and kinetic energy releases for the fragments have been determined. The spectra basically resemble available mass spectra obtained through electron impact (70 eV) demonstrating that the ionic dissociation of these compounds, induced by energetic electrons, is also dominated by processes involving low-energy valence-shell orbitals. A previously unreported fragment has been observed at m/z = 32 ( O 2 + ) in the spectra of valine and proline.