Time-of-flight measurements of hyperthermal Cl2 molecules produced by UV laser vaporization of cryogenic chlorine films

Abstract Time-of-flight distributions are obtained for the repetitive, unfocused laser vaporization of cryogenic Cl2 films condensed on a transparent substrate held at 25–110 K. Translationally fast molecules are observed using 193, 248, 351 and 355 nm, but no vaporization occurs for 532 or 1064 nm. The most probable kinetic energies of the Cl2 molecules, estimated from the maxima of the Cl2 time-of-flight traces, range from 0.4 to 2 eV for 193 nm vaporization at laser powers of 0.2–2 MW cm−2. The energies increase monotonically with increasing laser fluence and film thickness. Less than 7% of the desorbed flux is due to Cl atoms formed by dissociation in the desorption process. Energies above 5 eV are obtained with focused 355 nm radiation.