On the electronic structure and dynamical aspects of the predissociation of theAthinsp;2Pgr;OHgr;states of MgCl. A rigorous quantum mechanical treatment incorporating spinndash;orbit and derivative coupling effects

摘要

The nonadiabatic electronic structure and decay mechanisms of the spectroscopically analyzedAthinsp;2Pgr; state of MgCl are studied using a unique combination of rigorousabinitioelectronic structure and quantum dynamics techniques. The electronic structure treatment is based onabinitiomulticonfiguration selfhyphen;consistent field/first order and secondhyphen;order configuration interaction wave functions lsqb;PSgr;aJ(r;R)rsqb; for the 1,2thinsp;2Pgr;adiabaticelectronic states. These wave functions are used to determinerigorousdiabatic state wave functions using the derivative coupling matrix elements,gaJ,I(R)=lang;PSgr;aJ(r;R) Verbar;(part;/part;R)PSgr;aI(r;R)rang;r, and approximate diabatic state wave functions using a diabatization procedure based on diagonalizing the dipole moment operator suggested by Werner and Meyer lsqb;J. Chem. Phys.74, 5802 (1981)rsqb;. Near its equilibrium geometry theAthinsp;2Pgr;OHgr;state is well characterized as a regular diabatic state corresponding to Mg+(2P)hyphen;Clminus;(1S).The higher vibrational levels of this state are significantly perturbed (predissociated) by the interaction with a second inverted, dissociative, diabatic state of the same symmetry corresponding to Mg0(1S)Cl0(2P). Because the fine structure splitting,E(2thinsp;2Pgr;3/2)ndash;E(2thinsp;2Pgr;1/2), of the predissociating state is comparable to the vibrational spacing of the predissociated state, relativistic, spinndash;orbit, effects must be incorporated into the treatment of the predissociation. These relativistic effects are treated using the full microscopic Breitndash;Pauli spinndash;orbit (that is spinndash;orbit and spinndash;otherndash;orbit contributions) operator. The coupled diabatic state representation incorporating relativistic effects is used as the basis for semiclassical and fully quantum mechanical treatments of the predissociation lifetimes and energy shifts of theAthinsp;2Pgr;3/2,1/2vibrational states. By correctly taking into account the mixing of the regular and inverted 1,2thinsp;2Pgr; states the coupled state quantum scattering calculations are able to reproduce the observed lsquo;lsquo;anomalousrsquo;rsquo; dependence of the fine structure splitting factorAsov.