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)(v(1)v(2)) is presented for (v(1)v(2))=(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 v(1)=3940.6 cm(-1) and v(2)=3896.4 cm(-1). These values are somewhat larger than the corresponding experimental measurement of 3930.9 cm(-1) for v(1) and 3868.3 cm(-1) for v(2). The overtone frequencies are calculated to be 2v(1)=7713.5 cm(-1), 2v(2)=7642.5 cm(-1), and v(1) + v(2)=7841.8 cm(-1). The theoretical tunneling splittings of the fundamentals v(2) and v(1) 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), 2v(1), and v(1) + v(2) 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. (C) 1995 American Institute of Physics.