Dissociation rate constant of the hydrogen fluoride dimer by the ab initio anharmonic RRKM theory.

The dissociation rate constants for hydrogen fluoride dimers are calculated using the YL method, proposed by Yao and Lin (Yao, L.; Mebel, A. M.; Lu, H. F.; Neusser, H. J.; Lin, S. H. J. Phys. Chem. A 2007, 111, 6722). The dividing surface method and RRKM theory are also used to obtain pseudo-transition states and rate constants, respectively. For the dissociation of HF dimers, the anharmonic rate constants are around 3.02 x 10(10) to 3.46 x 10(12) s(-1), while the harmonic rate constants are in the range of 2.93 x 10(10) to 1.66 x 10(13) s(-1), at a temperature range of 243-1000 K, for the canonical case. For the microcanonical case, the anharmonic rate constants are in the range of 1.91 x 10(12) to 1.32 x 10(13) s(-1) and the harmonic rate constants are in the range of 1.89 x 10(12) to 4.93 x 10(13) s(-1), with a total energy range of 1338-4500 cm(-1). Both harmonic and anharmonic rate constants are only comparable to the experimental results 0.5 x 10(10) s(-1) and 1 x 10(11) s(-1) in an inert gas bath at room temperature. In this case the harmonic and anharmonic rate constants show similar results in this calculation. The results of this paper indicate that the YL method is suitable for calculating dissociation rate constants of small flexible HF dimers and the anharmonic effect should be included.