Abstract
The interaction potential energy surfaces for CN(X 2∑+, A 2∏)+He have been computed from ab initio MCSCF and MCSCF‐CI wave functions using an extensive basis set. In the presence of the He atom the two degenerate components of the CN⁺∏ state split into wave functions of A′ and A″ symmetry, and the symmetry of the 2∑+ state reduces to A′. The two adiabatic potentials for the A′ states are transformed to a diabatic basis, which yields a fourth potential energy surface V1, describing the collision‐induced electrostatic coupling between the two A′ states. The degree of mixing of the two diabatic A′ states has been determined by integration of the relevant nonadiabtic coupling matrix elements and, in a simpler method, from the coefficients of the MCSCF configurations. Both procedures yield virtually identical results. The nonadiabatic coupling matrix elements are strongly peaked near the CN bond distance at which the X 2∑+ and A 2∏ states cross in the isolated molecule. The diabatic coupling potential V1, however, is only weakly dependent on the CN bond distance, and decreases exponentially with the CN–He separation. Near the classical turning points for room temperature collisions the magnitude of V1 is approximately 50 cm−1. The V1 potential shows a bimodal character as a function of the collision angle θ. These results are discussed in connection with recent experiments of Dagdigian and co‐workers.
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