The three lowest ion-pair states of ICl

The three lowest ion-pair states of the iodine chloride molecule, E(Ω = 0), β(Ω = 1), and D′(Ω = 2), form a coupled triad whose Te'S all lie within 50 cm−1. Transitions to low vibrational levels (ν = 0–2) of D′ are reported for the first time and the analysis of E and β at low ν is expanded considerably. By including the coupling matrix elements explicitly in a nonlinear least squares fit, values for the electronic matrix elements are found that are close to, but slightly less than, the pure precession values.