Reaction probabilities of hot hydrogen atoms with CO2 and N2O

Abstract

Hot H atoms (H*) from the photodissociation of HI in the gas phase react with CO₂ according to H*+ CO₂→ OH + CO and with N₂O according to H*+ N₂O → NH + NO. Exciting light from a Xe flash lamp in a silica envelope led to H* with an average initial energy of 57 kcal/mol. Experimental yields of NH⁺ ₄, the ultimate product following (2), and of CO were analysed kinetically and the following relative reaction probabilities deduced: k_1a/(k_1a+k_1c)= 0.021₉ and k_2a/(k_2a+k_2c)= 0.010₄ where subscript “a” refers to reaction and subscript “c” refers to collisional cooling without reaction. Effects of added He and Ar allowed estimation of the relative numbers of collisions needed to cool H* to energy just below that for reaction; N_{CO2 /NHe and NCO2 /NAr are 1.8 and 0.49, respectively, indicating that, if the rare gases are acting as hard spheres, collisions of H* with CO2 are inelastic. Reaction and cooling parameters in the theory of Wolfgang and Estrup are also evaluated from the data. The kinetic treatment was also used to derive reaction efficiencies per collision of 0.197 and 0.607 for H*+ HI → H2+ I and H*+ I2→ HI + I, respectively.}