Adiabatic rotation, centrifugal sudden, and exact calculations of rotationally mediated Fermi resonances in HOCl

We investigate rotation-induced Fermi resonances in HOCl by the adiabatic rotation (AR), centrifugal sudden (CS), and exact methods, using a highly accurate potential energy surface [Skokov, S.; Peterson, K. A.; Bowman, J. M. Chem. Phys. Lett. 1999, 312, 494]. We focus on the rotationally mediated interaction between the (2,3,3) and (3,2,0) (nu (OH),nu (bend),nu (OCl)) states in the K = 4 subband using exact, AR, and CS methods. A simple two-state model is used to analyze the interaction, and interaction parameters are determined and compared with those of the experiment. A similar analysis is done for the high-energy interacting pair of states (4,0,0) and (3,2,1), using the AR method, and good agreement with the experiment is found. The comparison between AR calculations and the experiment for the metastable (6,0,0) and (4,4,2) states in the K = 0 subband shows good agreement for the value of J where zero-order states cross but not for the coupling constant. We also study rotationally mediated coupling in the pairs of states (1,0,2) and (0,3,2), (1,1,1) and (1,4,1), and (3,0,0) and (2,1,3) using exact and approximate methods. These interactions have not been studied experimentally.