6D quantum calculation of energy levels for HF stretching excited (HF)2

Abstract

Converged full-dimensional (6D) quantum mechanical calculation of energy levels of intramolecular stretching excited (HF)2(ν1ν2) is presented for (ν1ν2)=(01), (10), (02), (20), and (11). The bound state calculation for the excited HF dimer employs the SQSBDE potential energy surface of Quack and Suhm and is for total angular momentum J=0. This calculation provides the first rigorous theoretical result of energy levels for HF stretching excited HF dimer in full dimensions. The calculated fundamental transition frequencies are ν1=3940.6 cm−1 and ν2=3896.4 cm−1. These values are somewhat larger than the corresponding experimental measurement of 3930.9 cm−1 for ν1 and 3868.3 cm−1 for ν2. The overtone frequencies are calculated to be 2ν1=7713.5 cm−1, 2ν2=7642.5 cm−1, and ν1+ν2=7841.8 cm−1. The theoretical tunneling splittings of the fundamentals ν2 and ν1 are, respectively, a factor of 5.3 and 3.7 smaller than the ground state splitting, compared to a factor of 3 from the experimental measurement. The splittings of the overtone states 2ν2, 2ν1, and ν1+ν2 are smaller than that of the ground state by factors of 9.6, 48, and 1.8, respectively. Some of the calculated energy levels of excited (HF)2 are spectroscopically characterized and assigned.