Infrared Chemiluminescence Study of the Reaction of Hydroxyl Radical with Formamide and the Secondary Unimolecular Reaction of Chemically Activated Carbamic Acid

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.