On the quenching of helium 2thinsp;3S: Potential energy curves for, and nonadiabatic, relativistic, and radiative couplings between, theathinsp;3Sgr;+u,Athinsp;1Sgr;+u,bthinsp;3Pgr;g,Bthinsp;1Pgr;g,cthinsp;3Sgr;+g, andCthinsp;1Sgr;+gstates of He2

摘要

This work considers the possible role of nonadiabatic effects in the collisional quenching of He(2thinsp;3S). The electronic structure aspects of a nonadiabatichyphen;radiative decay mechanism are analyzed. In this mechanism theathinsp;3Sgr;+ustate is coupled by relativistic, rotational, and radiative interactions to theAthinsp;1Sgr;+ustate which serves as a gateway to theXthinsp;1Sgr;+g(electronically quenched) state of He2through the spinhyphen;allowed dipolehyphen;allowed boundndash;free transitionAthinsp;1Sgr;+urarr;Xthinsp;1Sgr;+g. State averaged MCSCF/secondhyphen;order CI wave functions for the groundXthinsp;1Sgr;+gstate, and the excited,athinsp;3Sgr;+u,Athinsp;1Sgr;+u,bthinsp;3Pgr;g,Bthinsp;1Pgr;g,cthinsp;3Sgr;+g, andCthinsp;1Sgr;+gstates (referred to here as the primary space) of He2were determined. Using thesewave functions all interstate matrix elements of the form lang;PSgr;0(J)Verbar;Ocirc;Verbar;PSgr;0(I)rang; were determined for (i)Ocirc;=Hcirc;BPequiv;Hcirc;so+Hcirc;sswhereHcirc;soandHcirc;ssare, respectively, the spinndash;orbit and dipolar spinndash;spin interactions in the Breitndash;Pauli approximation, (ii)Ocirc;=Lcirc;e, whereLcirc;eis the total electronic orbital angular momentum operator, and (iii)Ocirc;=mgr;circ; where mgr;circ; is the dipole moment operator. In the nonrotating molecule these interactions give rise to the spinhyphen;forbidden dipolehyphen;allowed radiative transitions (bthinsp;3Pgr;g,cthinsp;3Sgr;+g) rarr;Athinsp;1Sgr;+u. However a complete description of these radiative decay processes requires consideration of interactions originating outside the primary space. Thus in this work the spinhyphen;forbidden, dipolehyphen;allowed perpendicular, mgr;perp;(J,thinsp;Athinsp;1Sgr;+u0+), thinsp;J=cthinsp;3Sgr;+g1,thinsp;bthinsp;3Pgr;g1and parallel, mgr;par;(bthinsp;3Pgr;g0+,thinsp;Athinsp;1Sgr;+u0+), transition moments were determined using quasidegenerate perturbation theory. The computed potential energy curves, coupling matrix elements, and dipole moments permit a fully quantum mechanical analysis of the nonadiabatichyphen;radiative quenching mechanism. A preliminary phenomenological analysis of aspects of this process is provided.