Quantum Chemical Modeling of Astrophysical Ice Mantle Reactions of C ⁺ with Ammonia, Cyanamide, Formamide, Hydroxylamine, and Carbamic Acid

Reactions of low-energy cations with constituents adsorbed on icy grain mantles result in new pathways to significant compounds in the interstellar medium and protostellar nebulae. The present work characterizes reactions that can occur when the C+ cation in its ground state reacts with five nitrogen-containing molecules adsorbed onto amorphous ice cluster models: ammonia (NH3) and four NH2X amides: cyanamide (NH2CN), formamide (NH2CHO), hydroxylamine (NH2OH), and carbamic acid (NH2COOH), which are all either known or plausible astromolecules. Density functional theory calculations were performed using clusters containing 15–26 water molecules plus reactants. Vibrational spectra were generated for the five nitrogen-containing molecules adsorbed on amorphous ice, and reactions with C+ were characterized. In addition to identifying the variety of compounds that initially form from C+ addition, subsequent reactions of hydrogen atoms with radical intermediates were also characterized. Some of the products include known astromolecules or derivatives thereof, including H2NC, methanimine (CH2NH), protonated methanimine (CH2NH2+), 2-aminoketene, 2-iminoacetaldehyde, NH2, isocyanic acid (HNCO), hydrogen isocyanide (HNC), and others. In addition, a number of the H adducts are exotic carbene species that may potentially be detectable in astrophysical environments.