Infrared Chemiluminescence Study of the Reaction of Hydroxyl Radical with Formamide and the Secondary Unimolecular Reaction of Chemically Activated Carbamic Acid
journal contributionposted on 2018-04-03, 00:00 authored by N. I. Butkovskaya, D. W. Setser
Reactions of OH and OD radicals with NH2CHO and ND2CHO were studied by Fourier transform infrared emission spectroscopy of the product molecules from a fast-flow reactor at 298 K. Vibrational distributions of the HOD and H2O molecules from the primary reactions with the C–H bond were obtained by computer simulation of the emission spectra. The vibrational distributions resemble those for other direct H atom abstraction reactions, such as with acetaldehyde. The highest observed level gives an estimate of the C–H bond dissociation energy in formamide of 90.5 ± 1.3 kcal mol–1. Observation of CO2, ammonia, and secondary water chemiluminescence gave evidence that recombination of OH and NH2CO forms carbamic acid (NH2COOH) with excitation energy of 103 kcal mol–1, which decomposes through two pathways forming either NH3 + CO2 or H2O + HNCO. The branching fraction for ammonia formation was estimated to be 2–3 times larger than formation of water. This observation was confirmed by RRKM calculation of the decomposition rate constants. A new simulation method was developed to analyze infrared emission from NH3, NH2D, ND2H, and ND3. Dynamical aspects of the primary and secondary reactions are discussed based on the vibrational distributions of CO2 and those of H/D isotopes of water and ammonia.