Infrared chemiluminescence: Evidence for adduct formation in the H + CH2XI reaction and studies of the N + CH2X (X = Cl/F/I/H) reactions
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.