Lifetime measurements by ion translational energy spectrometry: metastable SH²⁺ ions

Abstract

Ion translational energy spectrometry has been used to determine the lifetime against spontaneous (unimolecular) dissociation of doubly charged molecular ions by studying the kinetic energies of fragment ions. Analysis of the shapes of the fragment ion kinetic energy distributions yields information on the lifetime of the precursor molecular ion. A value of 0.75+or-0.25 mu s is deduced for the lifetime of SH²⁺ ions. Correlation of this value with the shapes of calculated potential energy curves of low-lying electronic states of SH²⁺ enables deductions to be made of the importance of spin-orbit induced coupling between the lowest ⁴ Sigma ^- and ² Pi states and provides information on the vibrational level population in the doubly charged molecular ion.