Mode Selective Stereomutation and Parity Violation in Disulfane Isotopomers H2S2, D2S2, T2S2

Abstract

We report quantitative calculations of stereomutation tunneling in the disulfane isotopomers H2S2, D2S2, and T2S2, which are chiral in their equilibrium geometry. The quasi-adiabatic channel, quasi-harmonic reaction path Hamiltonian approach used here treats stereomutation including all internal degrees of freedom. The torsional motion is handled as an anharmonic reaction coordinate in detail, whereas all the remaining degrees of freedom are taken into account approximately. We predict how stereomutation is catalyzed or inhibited by excitation of the various vibrational modes. The agreement of our theoretical results with spectroscopic data from the literature on H2S2 and D2S2 is excellent. We furthermore predict the influence of parity violation on stereomutation as characterized approximately by the ratio (ΔEpv/ΔE±) of the (local or vibrationally averaged) parity violating potential ΔEpv and the tunneling splittings ΔE± in the symmetrical case. This ratio is exceedingly small for the reference molecules H2O2 and D2O2, and still very small (2⋅10−6 cm−1) for H2S2, which, thus, all exhibit essentially parity conservation in the dynamics. However, for D2S2 it is ca. 0.002, and for T2S2 it is ca. 1, which seems to be the first case where such intermediate mixing through parity violation is quantitatively predicted for spectroscopically accessible molecules. The consequences for the spectroscopic detection of molecular parity violation are discussed briefly also in relation to other molecules.