Photofragment fluorescence polarization following photolysis of HgBr2 at 193 nm

When HgBr2 (2–45 mTorr) is photolyzed by the linearly polarized output of an ArF excimer laser (193 nm), the visible emission from the HgBr B 2Σ+ fragment is found to be linearly polarized. The degree of polarization is 11.9%±1.5%, in close agreement with the theoretical value of 14.3% predicted for a 1Σg+(1A1) →1B2(1Σu+) dissociative transition in HgBr2. The addition of inert gases depolarizes the HgBr* emission. A simple model, developed to calculate the average angle through which the angular momentum vector of the HgBr* fragment is tipped by each hard sphere collision, fits well the pressure dependence of the depolarization.