Mass spectrometric studies on hydrogen-bonded clusters produced via supersonic expansions. IV. Temperature-dependent fragmentations in the electron-impact ionization of acetic acid dimer and trimer

Abstract

Molecular beams containing acetic acid dimer and trimer as major species were produced via supersonic expansions. Four ions at m/ z 105, 61, 103, and 121 generated by electron-impact ionization of the dimer and trimer were investigated as a function of the stagnation conditions and the ion injection energy, by which the cluster temperatures and the times of flight of these ions passing through a quadrupole mass analyser ( t 105, etc.) were varied, respectively. As a result, the temperature-dependent fragmentations of the dimer to the m/ z 105 ion and of the trimer to the m/ z 121 ion were found. This can be described in terms of the dependence of the lifetimes of these ions on the temperatures of the parent clusters. The temperature-dependent lifetime of the m/ z 105 ion was estimated to be of the order of 10 −4 s, comparable with t 105. Possible structures of these ions and their energetics are discussed.