A K-dependent adiabatic approximation to the Renner-Teller effect for triatomic molecules

A K-dependent adiabatic approach to studying the Renner-Teller effect of triatomic molecules was derived. The approach was applied to the Ã←X̃ transition spectrum of HCBr/DCBr. New adjusted MRCI/cc-pVTZ ab initio potential energy surfaces were employed in the calculations. Comparison with the observed spectra shows the numerical results from the K-dependent adiabatic method are reliable and accurate. Calculations explicitly show how the Renner-Teller effect has a profound effect on the ro-vibronic spectrum of the à state due to the small barrier height to linearity.