Reaction rate of H atoms with N2O in hot water

Abstract

The rate constant of H• atoms with N2O in water has been measured by a competition method up to 300°C. Radiolysis with 2.5MeV electrons generated H• atoms, and the HD product from their reaction with deuterated tetrahydrofuran (THF-d8) was measured with mass spectroscopy. The concentration of THF-d8 was changed by an order of magnitude in the presence of 25mM N2O to obtain the ratio of rate constants. To determine the rate constant of H• with THF-d8, a similar competition vs. 0.2mM OH– ion was also measured. The reaction rate of H• with OH– has been accurately determined vs. temperature in previous work, allowing the two unknown rate constants to be deduced. Rate constant of H• with THF-d8 follows the Arrhenius law ln(k/M−1s−1)=27.33 - (32.30kJ/mol)/RT. Rate constant of H• with N2O follows the Arrhenius law ln(k/M−1s−1)=24.50 - (30.42kJ/mol)/RT. In all likelihood, the N2O reaction proceeds via cis-HNNO• radical intermediate as in the gas phase, but with participation of a bridging water molecule in the 1,3 hydrogen shift to form N2 and •OH products.