VERY LOW-PRESSURE REACTOR CHEMILUMINESCENCE STUDIES ON N ATOM REACTIONS WITH CHCL3 AND CDCL3

Ground-state (N(S4)) nitrogen atom reactions with chloroform-h and chloroform-d were studied by using the VLPR technique at room temperature. Relative N atom concentrations were monitored via mass spectrometry, and their absolute values were determined by the chemical titration reaction with nitric oxide. It was possible to obtain a more accurate rate constant for the bimolecular reaction: N + NO --> N2 + O, k(NO) = (2.4 +/- 0.2) x 10(-11) cm3 molecule-1 s-1 at 298 K. N atom decay in the presence of CHCl3 and CDCl3 was found to have an apparent induction period and to have a large isotope effect. Chemiluminescence signals emitted from the reactor in the range of 300-600 nm were also observed, and identified as coming from the excited CN radical. The detailed study of reaction products, intermediates, N atom decay kinetics, and chemiluminescence signals are interpreted by a slow reaction of Cl atoms with CHCl3 followed by fast branching chain reactions of N atoms with the intermediate radicals. A successful numerical simulation of the experimental results supports the suggested chain branching mechanism. The following rate constants were estimated from the experimental results: k1(N + CHCl3 --> NCl + CHCl2), 1.00 x 10(-16), k2(N + NCl --> N + Cl), 2.57 x 10(-11), k3(Cl + CHCl3 --> HCl + CCl3), 3.70 x 10(-14), k3D(Cl + CDCl3 --> DCl + CCl3), 0.95 x 10(-14), k4(N + CHCl2 --> HCN + 2Cl), 1.98 x 10(-11), k5(N + CCl3 --> ClCN + 2Cl), 1.67 x 10(-11), k6(N + ClCN --> CCl + N2), 1.00 x 10(-14), and k7(N + CCl --> CN(B2-SIGMA-u+) + Cl), 5.70 x 10(-13), all in the units of cm3 molecule-1 s-1.