Knowledge Bank

Fermi resonance effects on Renner-Teller coupling in $NH2$ and $CH2$ have been identified. We have developed an extension of the semi-rigid bender approach of Jungen and Merer and of Duxbury and Dixon to calculate the interplay between Renner-Teller and vibrational resonances in detail. The basic idea is that if in the semi-rigid bender the bond length relaxes to follow the minimum on the potential energy surface, the effect of the stretch-bend coupling should be minimised in this basis. This should simplify the calculations compared to those using a full three dimensional basis when only a few quanta of the stretching vibrations are excited via resonances. The effects of the interplay between Renner-Teller and vibrational coupling wiill be discussed using some of the most recent data obtained for the $b¯$ state of $CH2$, making use of two-dimensional wavefunctions without and with Fermi resonance effects.