Experimental and computational studies of the kinetics of the reaction of hydrogen peroxide with the amidogen radical.

ABSTRACT

The pulsed-laser photolysis/laser-induced fluorescence method is used to study the kinetics of the reaction of NH2 with H2O2 to yield a second-order rate constant of (2.42 ± 0.55) × 10-14 cm3 molecule-1 s-1 at 412 K in 10-22 mbar of Ar bath gas. There are no prior measurements for comparison. To check this value and enable reliable extrapolation to other temperatures, we also compute thermal rate constants for this process over the temperature range 298-3000 K via multi-structural canonical variational transition-state theory with small-curvature multidimensional tunneling (MS-CVT/SCT). The CVT/SCT rate constants are derived using a dual-level direct dynamics approach utilizing single-point CCSD(T)-F12b/cc-pVQZ-F12 energies-corrected for core-valence and scalar relativistic effects-and M06-2X/MG3S geometries, gradients, and Hessians-for all stationary and non-stationary points along the reaction path. The multistructural method with torsional anharmonicity, based on a coupled torsional potential, is then employed to calculate correction factors for the rate constants, accounting for the comprehensive effects of torsional anharmonicity on the kinetics of this reaction system. The final MS-CVT/SCT rate constants are found to be in good agreement with our measurements and can be expressed in modified Arrhenius form as 2.13 × 10-15 (T/298 K)4.02 exp(-513 K/T) cm3 molecule-1 s-1 over the temperature range of 298-3000 K.