Renner-Teller induced predissociation of HNO((A)over-tilde (1)A ''): Rotational-state dependent linewidths of quasibound states

The predissociation dynamics in the (A) over tilde (1)A" electronic state o f HNO is investigated. The quantum mechanical dynamics calculations take in to account the Renner-Teller (or electronic Coriolis) coupling with the ele ctronic ground state (X) over tilde (1)A", which appears to be the dominant decay mechanism for the quasi-bound vibrational states in the (A) over til de (1)A" upper state. All three internal vibrational degrees of freedom are incorporated and two ab initio potential energy surfaces are used. The lin ewidths, Gamma, are directly calculated by the filter diagonalization metho d and an absorbing optical potential in the exit channel. They are generall y small (similar to1 cm(-1)) and increase with excitation of the bending mo de (bent-to-bent transition). On average, Gamma increases with K, the a-axi s rotational quantum number. However, for some vibrational states the linew idth shows a non-monotonic behavior with K, which is the result of mixing w ith highly excited vibrational levels in the continuum of the ground electr onic state. This effect is even more striking, when the total angular momen tum quantum number J is varied: In some cases, the linewidth exhibits a pro nounced resonancelike behavior as function of J. The agreement with recent experimental spectroscopic data is satisfactory. The calculated linewidths are of the same order (within a factor of 2 or so) as the experimental ones . However, because the two ab initio potential energy surfaces do not repro duce sufficiently well the (X) over tilde-(A) over tilde excitation energie s, the resonancelike effects are not quantitatively described. Potential en ergy surfaces with considerably higher accuracy are required. (C) 2001 Amer ican Institute of Physics.