Mode-selective stereomutation tunneling and parity violation in HOClH+ and H2Te2 isotopomers

Abstract

We investigate the stereomutation tunneling processes in the axially chiral prototype ion HOClH+ and in H2Te2 isotopomers in their relation to parity violation using quantum chemical calculations including our recently developed MC-LR approach to electroweak quantum chemistry and the quasiadiabatic channel reaction path Hamiltonian (RPH) approach. All the molecules dealt with here exhibit intermediate barriers to stereomutation (in the range from 0.1 to 0.3eV depending on the molecule and cis- or trans-type of transition structure considered). Whereas tunneling dominates the quantum dynamics of stereomutation in all isotopomers of HOClH+, the ground-state torsional tunneling splittings for hydrogen ditelluride isotopomers D2Te2 and T2Te2 are calculated to be much smaller than the parity violating energy differences ΔEpv between the enantiomers of these molecules. We present a systematic investigation of the dependence of tunneling splittings upon the excitation of various vibrational modes and we identify some strongly promoting and some weakly inhibiting modes as well as essentially inactive modes. A comparison of the new results for HOClH+ with our previous results for the isoelectronic HSOH shows some similarities but also some striking differences. HOClH+ is predicted to have sufficient kinetic stability for a spectroscopic observation, as a barrier of more than 1eV separates it from the more stable isomer H2OCl+. We also provide a summary comparing the whole series of axially chiral HXYH(+) isotopomers with X, Y=O, S, Se, Te, Cl and discuss the outlook for experiments on molecular parity violation in this series of molecular and ionic species. For the hydrogenic compounds D2Te2 is the only non-radioactive compound, in which parity violation is predicted to dominate over tunneling, similar to the chlorinated species Cl2S2, which we had investigated earlier.