Excited-state absorption in HgBr

The photoabsorption spectrum of the lowest ion pair state (B ²_Σ⁺1/2) of HgBr has been measured in the visible and ultraviolet (280≤λ≤480 nm) by laser excitation spectroscopy. Several previously unreported bands, peaking at 289, 302, 318, 330, 340, 364-373, and 401 nm, are observed and provide a stringent test for ab initio calculations of the excited state interaction potentials for the diatomic radical. A highly structured band lying between ∼444 and 470 nm confirms the observations of D. P. Greene, K. P. Killeen, and J. G. Eden [J. Chem. Phys. 85, 3188 (1986)] in a laser discharge. Also, the spectra fully resolve the apparent discrepancy between recent, unsuccessful attempts to produce a HgBr laser by flashlamp pumping the B←X band and experiments in which short pulse (8-25 ns) laser excitation of this transition has generated 502 nm coherent radiation with an energy conversion efficiency exceeding 20% [D. P. Greene, K. P. Killeen and J. G. Eden, Appl. Phys. Lett. 48, 1175 (1986)].