Renner-Teller and spin-orbit interactions between the1A1,1B1and3B1states of CH2

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Abstract
The [btilde]1B1-ã1A1 spectrum of the CH2 radical exhibits singlet-triplet perturbation of the ã and the [btilde] states, even though the direct first-order interaction between the [btilde]1B1 and [Xtilde]3B1 states is forbidden. We have derived a model for such interactions that involves both Renner-Teller and spin-orbit coupling. The results of calculations made using this model show that the effect of the Renner-Teller coupling is to generate 1B1-3B1 interactions that are as large as those between the 1A1 and 3B1 states. These effects are much larger than those normally expected when second-order singlet-triplet coupling occurs. From these calculations, we have identified the triplet-state levels responsible for the [btilde]-[Xtilde] perturbations, and have refined the triplet-state potential.