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

E. Arunan, S. P. Vijayalakshmi, R. Valera, D. W. Setser
2001 Physical Chemistry, Chemical Physics - PCCP  
Infrared chemiluminescence from a flow reactor has been used to study the H þ CH 2 XI and N þ CH 2 X (X ¼ Cl, F, I, H) reactions at 300 K. Both the HI þ CH 2 Cl and HCl þ CH 2 I channels were identified for the H þ CH 2 ClI reaction. The HCl channel involves adduct, HICH 2 Cl, formation as confirmed by the D þ CH 2 ClI reaction, which gave both HCl and DCl products. The nascent HCl(v) distribution from the H þ CH 2 ClI reaction was P 1 -P 5 ¼ 25 : 29 : 26 : 13 : 7. The rate constant for the
more » ... v) formation channel is estimated to be 4 times smaller than that for the H þ Cl 2 reaction. The highest HCl(v) level observed from the H þ CH 2 ClI reaction implies that the C-Cl bond energy is 50.2 kJ mol À1 lower than that of the Cl-CH 3 bond, which is in modest agreement with recent theoretical estimates. The H þ CH 2 FI reaction gave a HF(v) distribution of P 1 -P 3 ¼ 77 : 15 : 8. The C-F bond energy in CH 2 FI is estimated to be 4 460.2 kJ mol À1 , based on the highest HF(v) level observed, the upper bound being the same as that of F-CH 3 . When N atoms are added to the flow reactor, the HCl(v) emission intensities from H þ CH 2 ClI increased by up to 2-fold, which is attributed to the N þ CH 2 Cl ! HCl þ HCN reaction. Concomitant weak emission from HCN and HNC could also be observed; however, the main product channel is thought to be NCH 2 þ Cl. Strong visible CN(A-X) emission was also observed when H=N=CH 2 XI were present in the reactor. If the CH 2 X radicals were produced by the F þ CH 3 X reaction in the presence of N atoms, similar results were obtained. The N þ CH 2 N reaction is proposed as the first step that leads to CN(A) formation with NCN as an intermediate. N ð 4 SÞ þ CH 3 ðX 2 A 00 2 Þ ! CH 3 NðX 3 A 2 Þ ! CH 2 N ðX 2 AÞ þ H ðÀ167:4Þ ðR3Þ ! HCN þ H 2 ðÀ489:5Þ ð R4Þ ! HCN þ H þ H ðÀ54:4Þ ð R5Þ
doi:10.1039/b108362g fatcat:xbsuvkvrpzfudkhrbbi2yzd754