An Experimental and Theoretical Investigation of the C((1)D) + N2 → C((3)P) + N2 Quenching Reaction at Low Temperature.

Abstract

The gas-phase quenching reaction C((1)D) + N2 → C((3)P) + N2 has been investigated experimentally over the temperature range 50-296 K using a supersonic flow reactor. C((1)D) atoms were produced in situ by the pulsed multiphoton dissociation of CBr4 precursor molecules. Rate constants for this process were measured using a chemical tracer method whereby the C((1)D) + H2 → CH + H reaction was employed to follow C((1)D) decays by monitoring vacuum ultraviolet laser-induced fluorescence of the atomic hydrogen product at 121.567 nm. The deactivation rates are seen to increase at lower temperature, indicating the likely influence of the CNN intermediate complex lifetime on intersystem crossing for this system. We also performed electronic structure calculations of relevant C((3)P)-N2 and C((1)D)-N2 potential energy curves as well as triplet-singlet spin-orbit coupling terms using the explicitly correlated internally contracted multireference configuration interaction method (ic-MRCI-F12). The calculations were performed for the collinear and perpendicular approach of the C atom toward the N2 molecule, which allowed us to construct the approximate spherical (isotropic) potential model of C-N2(j = 0). The computed reduced dimensional potentials were used in quantum close coupling scattering calculations of the electronic quenching cross sections and rate constants. While the calculated potential energy curves form the basis for a good qualitative description of the reaction, the calculated rate constants are significantly smaller than the measured ones, and fail to reproduce the temperature dependence of the experimental results. Several possible reasons are provided to explain the origin of these differences.