Spin-forbidden decay of the dication HS2+

Abstract

The lifetimes of the low-lying vibrational levels of the X2Π state of the recently identified dication HS2+ [Miller et al., Int. J. Mass Spectrom. Ion Proc. 100, 505 (1990)] are considered. The stability of this state is attributable to a barrier formed from the avoided crossing of 2Π states asymptotically characterized as H++S+ and H+S2+. As a result of this barrier, the nonrelativistic X2Π potential energy curve supports several quasibound vibrational levels that are long lived with respect to tunneling. However, this is not the principal decay mechanism. We show that the lifetimes of the low-lying vibrational levels, v=0−4, are controlled entirely by the spin–orbit induced perturbation, 14Σ−∼X2Π, and the corresponding allowed crossing of the X2Π potential energy curve by the dissociative 14Σ− potential energy curve which correlates with the ground state asymptote H++S+(4S).