Origin of the 454 nm bound→free absorption band of cadmium monoiodide (¹¹⁴CdI)

The bound→free absorption band recently observed in a ¹¹⁴CdI laser discharge [Greene and Eden, Opt. Comm. (1985)] is shown to arise from absorption by the B ²Σ excited state of ¹¹⁴CdI to a previously unobserved level lying ∼4.3×10 ⁴ cm^-1 above ground. Pumping of the absorptive transition with a pulsed blue dye laser strongly suppresses gain (and, hence, laser output power) on the B→X band in the red (657 nm). Therefore, this constitutes the first known report of an ionic excited state→covalent absorption band [i.e., (M⁺X^-)+ℏω→M*+X; M, X=metal and halogen atoms, respectively] for any of the group IIB metal halides or rare gas-halide laser molecules. Also, ω_e for the B ²Σ state of ¹¹⁴CdI is ≳ 110 cm^-1 (considerably larger than an existing value in the literature) and the terminal level for this blue absorption band is tentatively assigned to a dissociative ²Σ state correlated with the Cd(5p ³P_J)+I separated atom limit.