COMPARING EXPERIMENTAL AND CALCULATED SPECTRAL PARAMETERS FOR JAHN-TELLER ACTIVE MOLECULES. PART I

Great advances in quantum chemistry calculations for molecules over the last decade has left a cogent need to make theory testable by experiments. One area of fundamental interest is the computation of both spectroscopic and dynamical properties of molecules near conical intersections between different electronic states. Experiments on naturally occurring and spectroscopically accessible conical intersections in Jahn-Teller molecules provide excellent benchmarks for computations. This talk discusses an approach which allows direct computation of experimental parameters determined from rotationally resolved experiments. An Effective Rotational Hamiltonian (ERH) for Jahn-Teller active system with a $C_3$ or $C_5$ symmetry axis is presented. Methods for calculating the parameters of the ERH using electronic structure and vibrational mode data from coupled cluster calculations are reported. Furthermore theory is advanced to develop a prescription for obtaining observable rovibronic parameters like the rotational distortion parameter, $h_1$, and transition intensities for systems with a $C_3$ and $C_5$ symmetry axis. An important goal of these calculations is to compare experimentally observable parameters to those from highly developed theoretical tools presently available