Very-low-pressure-reactor chemiluminescence studies on nitrogen atom reactions with chloroform and deuteriochloroform

Abstract

Ground-state (N(S{sup 4})) 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 constant for the bimolecular reaction: N + NO {yields} N{sub 2} + O, k{sub NO} = (2.4 {plus minus} 0.2) {times} 10{sup {minus}11} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} at 298 {Kappa}. N atom decay in the presence of CHCl{sub 3} and CDCl{sub 3} 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 C1 atoms with CHCl{sub 3} 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: k{sub 1}(N +more » CHCl{sub 3} {yields} NCl + CHCl{sub 2}), 1.00 {times} 10{sup {minus}16}, k{sub 2}(N + NCl {yields} N + Cl), 2.57 {times} 10{sup {minus}11}, K{sub 3}(Cl + CHCl{sub 3} {yields} HCl + CCl{sub 3}), 3.70 {times} 10{sup {minus}14}, k{sub 3D}(Cl + CDCl{sub 3} {yields} DCl + CCl{sub 3}), 0.95 {times} 10{sup {minus}14}, and k{sub 7}(N + CCl {yields} CN(B{sup 2}{Sigma}{sup +}{sub u}) + Cl), 5.70 {times} 10{sup {minus}13}, all in the units of cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}.« less