Adiabatic and diabatic potential energy surfaces for collisions of CN(Xthinsp;2Sgr;+,thinsp;Athinsp;2Pgr;) with He

摘要

The interaction potential energy surfaces for CN(Xthinsp;2sum;+,thinsp;Athinsp;2prod;)+He have been computed fromabinitioMCSCF and MCSCFhyphen;CI wave functions using an extensive basis set. In the presence of the He atom the two degenerate components of the CNthinsp;2prod; state split into wave functions ofArsquo;andAlsquo;symmetry, and the symmetry of the2sum;+state reduces toArsquo;. The two adiabatic potentials for theArsquo;states are transformed to a diabatic basis, which yields a fourth potential energy surfaceV1, describing the collisionhyphen;induced electrostatic coupling between the twoArsquo;states. The degree of mixing of the two diabaticArsquo;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 theXthinsp;2sum;+andAthinsp;2prod; states cross in the isolated molecule. The diabatic coupling potentialV1, however, is only weakly dependent on the CN bond distance, and decreases exponentially with the CNndash;He separation. Near the classical turning points for room temperature collisions the magnitude ofV1is approximately 50 cmminus;1. TheV1potential shows a bimodal character as a function of the collision angle thgr;. These results are discussed in connection with recent experiments of Dagdigian and cohyphen;workers.