Vibrational distributions of HgBr(B 2Σ) and HgI(B 2Σ) molecules formed by photodissociation of HgBr2 and HgI2

Reliable fluorescence spectra (±3%) of HgBr and HgI photofragments formed in the direct photodissociation of HgBr2 and HgI2 at 193 nm have been measured. The nascent vibrational distributions of HgBr(B 2Σ) and HgI(B 2Σ) have been determined. The distributions are resolvable into the relative contributions from two processes: (1) hν+HgX2→HgX(B 2Σ) +X(2P3/2) and (2) hν+HgX2→HgX(B 2Σ)+X(2P1/2). HgX(B 2Σ) molecules formed with X(2P3/2) atoms exhibit vibrational population inversion and preferential energy disposal among the higher vibrational states. In contrast, the vibrational excitation of HgX(B 2Σ) molecules formed with X(2P1/2) atoms produces a Boltzmann-like distribution which strongly favors the lowest vibrational states.