Theoretical study of the Jahn-Teller effect in (X)over-tilde E-2 CH3O

The Jahn-Teller effect in (X) over tilde E-2 CH3O is theoretically investig ated in considerable detail. Making use of ab initio calculations carried o ut at the MRC-level we present the global shape of the adiabatic potential surfaces. Both sheets of the Jahn-Teller split (X) over tilde E-2 electroni c state are used to determine the linear, quadratic and bilinear coupling c onstants of the e and a(1) modes, as well as selected third-order constants . Dynamical calculations for the vibronic structure have been performed wit h these parameters. The dynamical Jahn-Teller problem is solved by taking i nto account all the three e modes or, alternatively, two e modes and two a( 1) modes. The resulting vibronic spectra are compared with those of previou s work. Furthermore, ab initio calculated transition moments for (A) over t ilde (2)A(1)<---->(X) over tilde E-2 are used to give an explanation for th e forbidden Delta j = 3/2 transitions which were found by different experim ental groups. (C) 2000 American Institute of Physics. [S0021-9606(00)30108- 8].