Is SH4, the simplest 10-S-4 sulfurane, observable?

The kinetic stability of SH4 was investigated theoretically with the couple d cluster ansatz. The two possible modes of decomposition into SH2 and H-2 through either a C-2v or a C-1 transition structure (TS) were investigated using intrinsic reaction coordinate (IRC) computations; orbital interaction s along the reaction paths were analyzed. The two dissociation modes are du e to differences in the electron delocalization in the TSs. While the C-2v TS is bonded rather covalently by a three center-four electron (3c-4e) inte raction which is lost in a strictly synchronous way (two electrons occupy t he same orbital at a time along the reaction coordinate), the bonding orbit al in the C-1 TS is merely occupied by a single electron. Surprisingly, thi s highly polarized TS has a lower barrier. Computations at the CCSD(T)/cc-p VQZ level of theory show that the zero-point corrected enthalpy (Delta H(0) double dagger) of the C-1 TS is 16 kcal mol(-1) above the C-4v symmetric gr ound state; the barrier along the C-2v path is 40 kcal mol(-1). The overall exothermicity for the dissociation into SH2 and H-2 was estimated to be De lta H-0 = -76 kcal mol(-1). The fundamental IR absorptions of SH4 (obtained by scaling the computed harmonic vibrational frequencies taken from the CC SD(T)/cc-pVQZ level of theory) are 1432 and 2037 cm(-1).