Theoretical studies of rotation induced Fermi resonances in HOCl

Theoretical investigations of rotation induced Fermi resonances in HOCl are carried out using several different quantum mechanical methods. Due to shape differences of the eigenfunctions, nearby vibrational levels may be energetically tuned to form Fermi (or anharmonic) resonances by varying rotational quantum numbers. Such rotation induced Fermi resonances have been observed experimentally in HOCl, for example, for bright states (3,2,0) and (4,0,0) by Abel [J. Chem. Phys. 104, 3189 (1996) and ibid. 106, 3103 (1997)]. Using an ab initio potential, this work shows that the (3,2,0) state is significantly mixed with the (2,3,3) state near J = 28 and K = 4, and J = 14 and K = 3, while the (4,0,0) state forms a Fermi pair with (3,2,1) near J = 43 and K = 8. The wave functions of the Fermi pairs display significant deformation due to the mixing. Both the rotation induced degeneracy and coupling strength are found to be important. (C) 1999 American Institute of Physics. [S0021-9606(99)02040-1].