Destruction route of solid-state formamide by thermal H atoms

Abstract

Context. Formamide (NH2CHO) is one of the simplest “CHON” molecules that has been observed in different environments in space. In star-forming regions, its abundance in the gas phase is correlated to isocyanic acid (HNCO), indicating a chemical relation between the two species. Many studies have investigated the different routes for the transformation of the two species from one to the other. Aims. We carry out an experimental analysis on the interaction of atomic H at 300 K with solid NH2CHO to probe whether HNCO can form. Methods. The effects of H atom irradiation on NH2CHO have been analyzed by Fourier-transform infrared spectroscopy. Results. During irradiation, a decrease in the band intensity of the C–H, C=O, and N–H modes of NH2CHO with a simultaneous increase in the N=C=O band intensity of HNCO is observed, indicating a transformation of NH2CHO to HNCO. The corresponding destruction and formation cross-sections have been estimated from the trend of the normalized column densities as a function of the H atom fluence. The transformation follows a three-step reaction sequence driven by H atom exothermic abstractions that also induce sputtering of the products. No bands of aminomethanol were detected. Conclusions. The interaction of H atoms with NH2CHO in space can be one of the promising mechanisms to explain the chemical relation between NH2CHO and HNCO. In addition, the comparison of our results with those of other energetic processing agents suggests that H atoms play a crucial role in the destruction of NH2CHO ice in dense regions of the interstellar medium.