Relaxation of 6 ²P_3/2 metastable and 6 ²P_1/2 ground state atomic thallium produced in the photodissociation of thallium halide vapors at high densities

Decay rates of the 6 ²P_3/2 metastable and 6 ²P_1/2 ground state atomic thallium densities produced in UV photodissociation (at λ 193, 222, 249, 308, and 353 nm) of TlI, TlBr, and TlCl molecular vapors have been measured for vapor densities from 10 ¹³ to 10¹⁷ cm^-3. Dominant relaxation processes have been identified as (i) for the metastable state, collisional deexcitation by thallium halide molecules at high halide densities (≥10¹⁵ cm^-3) and by free halogens and trace impurities at lower halide densities and (ii) for the ground state, diffusion in the ambient (argon/thallium halide) gas at high halide densities and volume reassociation under certain conditions at low halide densities. Cross sections and diffusion coefficients are evaluated.