THE EFFECTS OF VIBRATIONAL RESONANCES ON RENNER-TELLER COUPLING IN TRIATOMIC-MOLECULES - THE STRETCH-BENDER APPROACH

A vibration-rotation Hamiltonian for a symmetric triatomic molecule, b ased upon a stretch-bender reference frame has been derived. This fram e is chosen so that as the molecule bends the reference geometry follo ws the minimum in the potential energy surface, thus minimizing the si ze of the displacements required to reach the instantaneous axis geome try. This may be regarded as an extension of methods based upon the ri gid-bender reference frame approach developed by Hougen, Bunker, and J ohns [J. Mel. Spectrosc. 34, 136 (1970)]. This new stretch-bender Hami ltonian is combined with the Barrow, Dixon, and Duxbury [Mel. Phys. 27 , 1217 (1974)] and the Jungen and Merer [Mel. Phys. 40, 25 (1980)] met hods of solving the Renner-Teller coupling problem in which molecules execute large amplitude nuclear motion, producing a compact method for the variational calculation of the energies of such a system. The (a) over tilde (1)A(1) and (b) over tilde B-1(1) states of the methylene radical, CH2, are used to demonstrate the use of this method for the a nalysis of the behavior of strongly coupled electronic and vibrational states. (C) 1998 American Institute of Physics.