A phenomenological model for the vibrational dependence of hydrogen interchange tunneling in HF dimer

We present a phenomenological model to account for the observations of the hydrogen interchange tunneling at N = v(1) + v(2) = 1-3 of the fret (v(1)) and the bound (v(2)) HF stretches of (HF)(2). Good agreement is obtained between calculations and observations at the levels (v(1), v(2)) of v(1) - v(2) = +/-1 for both N = 1 and 3, suggesting that the observed hydrogen tunneling splittings in these levels are direct rather than the results of many extraneous perturbations. The model also predicts well the ratios of the rates of vibrational predissociation at these states, in addition to the splittings. We attribute the unusually large vibrational dependence of the splittings upon valence bond excitation to the result of interbond coupling between the two HF local oscillators. Significant differences in the vibrational energy of the level (1,2) as well as the tunneling splitting at (2,0) between observation and prediction are, however, noted. (C) 1996 American Institute of Physics.