HNS(+) and HSN(+) cations: Electronic states, spin-rovibronic spectroscopy with planetary and biological implications.

Ab initio methods in conjunction with a large basis set are used to compute the potential energy surfaces of the 12 lowest electronic states of the HNS(+) and HSN(+) isomeric forms. These potentials are used in discussions of the metastability of these cations and plausible mechanisms for the H(+)/H + SN(+)/SN, S/S(+) + NH(+)/NH, N/N(+) + SH(+)/SH ion-molecule reactions. Interestingly, the low rovibrational levels of HSN(+)(1(2)A″) and HNS(+)(1(2)A″) electronically excited ions are predicted to be long-lived. Both ions are suggested to be a suitable candidate for light-sensitive NO(⋅) donor in vivo and as a possible marker for the detection of intermediates in nitrites + H2S reactions at the cellular level. The full spin rovibronic levels of HNS(+) are presented, which may assist in the experimental identification of HNS(+) and HSN(+) ions and in elucidating their roles in astrophysical and biological media.