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

Converged full-dimensional (6D) quantum mechanical calculation of energy levels of intramolecular stretching excited (HF)₂(v₁v ₂) is presented for (v₁v₂) = (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 v₁ = 3940.6 cm ^-1 and v₂ = 3896.4 cm^-1. These values are somewhat larger than the corresponding experimental measurement of 3930.9 cm^-1 for v₁ and 3868.3 cm^-1 for v₂. The overtone frequencies are calculated to be 2v₁ = 7713.5 cm ^-1, 2v₂ = 7642.5 cm^-1, and v₁ + v₂ = 7841.8 cm^-1. The theoretical tunneling splittings of the fundamentals v₂ and v₁ 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 2v ₂, 2v₁, and v₁ + v₂ 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.