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The first experimental study of the low-temperature kinetics of the gas-phasereaction of NH2 with formaldehyde (CH2O) has been performed. This reaction haspreviously been suggested as a source of formamide (NH2CHO) in interstellarenvironments. A pulsed Laval nozzle equipped with laser-flash photolysis andlaser-induced fluorescence spectroscopy was used to create and monitor thetemporal decay of NH2 in the presence of CH2O. No loss of NH2 could be observedvia reaction with CH2O and we place an upper-limit on the rate coefficient of<6x10-12 cm3 molecule-1 s-1 at 34K. Ab initio calculations of the potentialenergy surface were combined with RRKM calculations to predict a ratecoefficient of 6.2x10-14 cm3 molecule-1 s-1 at 35K, consistent with theexperimental results. The presence of a significant barrier, 18 kJ mol-1, forthe formation of formamide as a product, means that only the H-abstractionchannel producing NH3 + CHO, in which the transfer of an H-atom can occur byquantum mechanical tunnelling through a 23 kJ mol-1 barrier, is open at lowtemperatures. These results are in contrast with a recent theoretical studywhich suggested that the reaction could proceed without a barrier and wastherefore a viable route to gas-phase formamide formation. The calculated ratecoefficients were used in an astrochemical model which demonstrated that thisreaction produces only negligible amounts of gas-phase formamide underinterstellar and circumstellar conditions. The reaction of NH2 with CH2O istherefore not an important source of formamide at low temperatures ininterstellar environments.

The gas-phase reaction of NH2 with formaldehyde (CH2O) is not a source of formamide (NH2CHO) in interstellar environments