QUANTUM-CHEMICAL STUDY OF THE POTENTIAL-ENERGY CURVES AND ELECTRONIC-TRANSITION STRENGTHS IN HCL, XECL, AND HCL+XE

Potential energy curves and electronic transition strengths are calcul ated for selected singlet states in HCl, XeCl, and HCl + Xe using effe ctive core potentials (ECPs) with state-averaged CASSCF-CI techniques. In HCl, the maximum photoabsorption cross section for the ($) over ti lde A((1) Pi) <-- ($) over tilde X((1) Sigma(+)) transition is calcula ted to be sigma(v'') 3.86 X 10(-18) cm(2) for the v'' = 0 band, in goo d agreement with the experimental value of sigma(v'') = 3.8 X 10(-18) cm(2). The oscillator strength for the 0-0 transition in ($) over tild e C((1) Pi) <-- ($) over tilde X((1) Sigma(+)) is calculated to be f(0 0) = 0.175, differing by 5% from the experimental value of f(00) = 0.1 85 +/- 0.037. The calculated oscillator strength for excitation into v ' = 1 is significantly larger than the experimental values or those fr om previous theoretical treatments. In the XeCl, radiative lifetimes, tau, are predicted for selected doublet excited electronic states. Thi s study substantiates earlier theoretical predictions and compares fav orably with available experimental lifetimes. In the HCl + Xe system, low-lying singlet states are calculated as a function of the HCl-Xe di stance with the H-Cl distance held fixed and the atoms kept collinear. A charge-transfer state is located which represents the excitation of a pi electron into a sigma antibonding orbital. This state offers a simplified model of the photoinitiated charge transfer observed in sol id xenon doped with HCl, where the HCl is reported to dissociated afte r transfer of an electron from Xe to HCl. Other electronic states and electronic transition moments of the HCl + Xe system are analyzed and related to the isolated HCl electronic states and transitions when pos sible.