Infrared chemiluminescence: evidence for adduct formation in the H+CH₂XI reaction and studies on the N+CH₂X reactions

Abstract

Infrared chemiluminescence from a flow reactor has been used to study the H+CH₂XI and N+CH₂X (X=Cl, F, I, H) reactions at 300 K. Both the HI+CH₂Cl and HCl+CH₂I channels were identified for the H+CH₂ClI reaction. The HCl channel involves adduct, HICH₂Cl, formation as confirmed by the D+CH₂ClI reaction, which gave both HCl and DCl products. The nascent HCl(v) distribution from the H+CH₂ClI reaction was P₁-P₅=25:29:26:13:7. The rate constant for the HCl(v) formation channel is estimated to be 4 times smaller than that for the H+Cl₂ reaction. The highest HCl(v) level observed from the H+CH₂ClI reaction implies that the C-Cl bond energy is 50.2 kJ mol⁻¹ lower than that of the Cl-CH₃ bond, which is in modest agreement with recent theoretical estimates. The H+CH₂FI reaction gave a HF(v) distribution of P₁-P₃=77:15:8. The C-F bond energy in CH₂FI is estimated to be ≤460.2 kJ mol⁻¹, based on the highest HF(v) level observed, the upper bound being the same as that of F-CH₃. When N atoms are added to the flow reactor, the HCl(v) emission intensities from H+CH₂ClI increased by up to 2-fold, which is attributed to the N+CH₂Cl→HCl+HCN reaction. Concomitant weak emission from HCN and HNC could also be observed; however, the main product channel is thought to be NCH₂+Cl. Strong visible CN(A-X) emission was also observed when H/N/CH₂XI were present in the reactor. If the CH₂X radicals were produced by the F+CH₃X reaction in the presence of N atoms, similar results were obtained. The N+CH₂N reaction is proposed as the first step that leads to CN(A) formation with NCN as an intermediate.