Results of the first full-dimensional (6D) quantum calculations of the vibrational levels of the v1 and v2 HCl-stretch excited (HCl)2, for total angular momentum J = 0, are presented. Three 6D potential energy surfaces (PESs) were employed. Two widely used PESs, the ab initio PES of Bunker and co-workers and the semiempirical PES by Elrod and Saykally, are found to give negligible tunneling splittings (≤5 × 10-2 cm-1) for the vibrational eigenstates of the v1/v2 excited (HCl)2, in sharp disagreement with the experimental tunneling splittings in the v1 and v2 fundamentals, -3.32 and 3.18 cm-1. In an effort to overcome this problem, a 6D electrostatic interaction potential is constructed and added to the ES1 PES; the resulting 6D PES is denoted ES1-EL. Quantum 6D calculations on the ES1-EL PES yield greatly improved tunneling splittings for v1 (-2.31 cm-1) and v2 (2.45 cm-1), which are 70% and 77%, respectively, of the corresponding experimental values. The v1 and v2 fundamental HCl-stretching frequencies calculated on the ES1-EL PES are only 5.9 cm-1 lower and 2.9 cm-1 higher, respectively, than their experimental counterparts. In addition, the quantum 6D calculations on the ES1-EL PES provide a comprehensive characterization of the v1/v2 supported vibrational eigenstates of (HCl)2, including their energies, assignments, and tunneling splittings. The vibration-rotation-tunneling dynamics of (HCl)2 in the v1 and v2 excited states which emerged from our calculations differs substantially from that observed for the HF-stretch excited (HF)2.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry