Depletion Kinetics of Mo(a7S3,a5S2,a5DJ) by N2, SO2, CO2, N2O, and NO

Abstract

The gas phase collisional disappearance of Mo(a7S3,a5S2,a5DJ) in the presence of N2, SO2, CO2, N2O, and NO over the temperature range 294−621 K and in the total pressure range 10−600 Torr is reported. Mo atoms were produced by the 248 nm photodissociation of Mo(CO)6 and MoCl4 and detected by laser-induced fluorescence. The room temperature depletion rate constant of Mo(a5S2) + N2 is (2.3 ± 0.7) × 10-11 cm3 s-1; the depletion rate constants of the a5DJ are smaller and range from (16 ± 8) × 10-12 for Mo(a5D0) to (0.13 ± 0.04) × 10-12 cm3 s-1 for the other spin−orbit states. The depletion rate of all states of Mo by SO2 are on the order of the collision rate. Mo(a7S3) is found to be unreactive toward CO2, and the rate constant for the reaction of Mo(a7S3) with N2O is expressed as k(T) = (2.0 ± 0.5) × 10-10 exp[−(9.8 ± 0.3) kcal mol-1/RT] cm3 s-1. Termolecular kinetics are observed for Mo(a7S3) + NO with k0 = (2.6 ± 0.3) × 10-29 cm6 s-1, k∞ = (5.8 ± 0.5) × 10-11 cm3 s-1, and Fc = 0.72 ± 0.07 at 296 K; the reaction rates for this reaction decrease with increasing temperature. Depletion rate constants of the reactions of the excited states of Mo with CO2, N2O, and NO are on the order of 10-12−10-10 cm3 s-1; the depletion kinetics are complex and involve significant energy transfers. Results indicate that the electron configuration of Mo plays a role in its depletion kinetics. In all cases, Mo(4d55s1a5S2) depletes faster than Mo(4d45s2a5DJ). The inefficient reactions of Mo(a7S3) with CO2 and N2O are attributed to the production of spin-forbidden states.