Complex L-2 calculation of the variation of resonance widths of HOCl with total angular momentum

Complex L-2 calculations of the variation of the resonance width of HOCl(6 nu(OH))--> Cl+OH with total angular momentum, J, are reported, using a recently developed, accurate ab initio potential energy surface [S. Skokov, J. M. Bowman, and K. A. Peterson, J. Chem. Phys. 109, 2662 (1998)]. The calculations are carried out using the adiabatic rotation approximation for the overall rotation and a truncation/recoupling method for the vibrational states. An ab initio calculation of the J and K dependence of the intensity of the absorption spectrum of the Q branch in the neighborhood of the 2 nu(OH)--> 6 nu(OH) transition is presented, and compared to results of recent experiments of Rizzo and co-workers. The variation of the resonance width of the 6,0,0 and the 3,8,0 states with J and K is presented, and comparisons with recent double-resonance experiments of the Rizzo and Sinha groups for the 6,0,0 state show encouraging qualitative agreement. The fluctuations of the dissociation rate with J is shown to be due to rotation-induced coupling of the 6 nu(OH) state to a dense set of highly excited OCl stretch states. A simple model describing the coupling of 6 nu(OH) with background states, using a coupling constant of 0.05 cm(-1) is shown to give a qualitatively correct picture of the fluctuation of the resonance width with J. Finally, the energies of many nonoverlapping resonances, some of which are assigned, for J=18 and K=0 are presented and compared to Rice-Ramsperger-Kassel-Marcus (RRKM) theory. It is found that due to slow, rate limiting, intramolecular vibrational relaxation the RRKM overestimates the average dissociation rate by an order of magnitude. (C) 1999 American Institute of Physics. [S0021-9606(99)01135-6].