Potential energy curves and electronic transition strengths are calculated for selected singlet states in HCl, XeCl, and HCl + Xe using effective core potentials (ECPs) with state-averaged CASSCF-CI techniques. In HCl, the maximum photoabsorption cross section for the ($) over tilde A((1) Pi) <-- ($) over tilde X((1) Sigma(+)) transition is calculated to be sigma(v") 3.86 X 10(-18) cm(2) for the v" = 0 band, in good agreement with the experimental value of sigma(v") = 3.8 X 10(-18) cm(2). The oscillator strength for the 0-0 transition in ($) over tilde C((1) Pi) <-- ($) over tilde X((1) Sigma(+)) is calculated to be f(00) = 0.175, differing by 5% from the experimental value of f(00) = 0.185 +/- 0.037. The calculated oscillator strength for excitation into v’ = 1 is significantly larger than the experimental values or those from previous theoretical treatments. In the XeCl, radiative lifetimes, tau, are predicted for selected doublet excited electronic states. This study substantiates earlier theoretical predictions and compares favorably with available experimental lifetimes. In the HCl + Xe system, low-lying singlet states are calculated as a function of the HCl-Xe distance 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 solid xenon doped with HCl, where the HCl is reported to dissociated after 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 possible.