SDCI and MRSDCI Studies of Four Low-Lying Electronic States of OCCO and Mechanism of Collisional Energy Transfer of CO （A¹π） and CO（X¹Σ）

The equilibrium geometries and excitation energies for four low—lying electronic states, X³Σ_g^-, a¹Δ_g, A³π_g and I¹π_g, of OCCO have been calculated at the SDCI level with a DZ+P basis set. The dissociation path of OCCO(1¹π_g) has been studied at the MRSDCI level with the same basis set. Based on our calculations we have discussed the formation of the complex（exciplex） of CO（A¹π） and CO（X¹Σ） by collinear collisions. Our calculation results for the exciplex OCCO* can explain the experimental fact of the very efficient CO（A¹π）→CO（X¹Σ） electronic energy transfer.