Reaction of Nitric Oxide and Ozone in Cryogenic Matrices. Quantum-Mechanical Tunneling and Vibrational Enhancement

Article abstract of DOI:10.1021/j150622a030

The cryogenic reaction between nitric oxide and ozone has been reexamined in solid nitrogen, argon, and krypton matrices at 6-20 K.In the absence of light, the kinetics of the growth of NO2 is close to first order but is more accurately represented by a superposition of two first-order processes.In a nitrogen matrix, NO/O3/N2=1:1:100, the closest first-order rate constant is 0.1 h^-1, and it is virtually temperature independent (6-16 K) provided the kinetics are measured at a temperature below the deposition temperature.The absence of temperature dependence and a significant 18O isotope effect on the rate indicate that heavy-atom tunneling is involved.When the NO in NO*O3 nearest-neighbor pairs is vibrationally excited with a CO laser, the rate constant increases linearly with the laser power.This shows that the rate is enhanced in the cryogenic environment by NO vibrational excitation (photon energy, 5.4 kcal mol^-1) in a one-photon process with low quantum yield.