An isomer-specific study of solid nitromethane decomposition pathways – Detection of aci-nitromethane (H2CNO(OH)) and nitrosomethanol (HOCH2NO) intermediates

Highlights: • We studied irradiated nitromethane ice with tunable ionization of products. • Aci-nitromethane reported in a condensed phase experiment for the first time. • Nitrosomethanol and, tentatively, 2-hydroxy-oxaziridine isomers observed. An isomer specific study of energetic electron exposed nitromethane ices was performed via photoionization – reflectron time of flight mass spectrometry (PI-ReTOF-MS) of the subliming products employing tunable vacuum ultraviolet light for ionization. Supported by electronic structure calculations, nitromethane (CH₃NO₂) was found to isomerize to methyl nitrite (CH₃ONO) and also via hydrogen migration to the hitherto elusive aci-nitromethane isomer (H₂CNO(OH)). The latter isomerizes to nitrosomethanol (HOCH₂NO) through hydroxyl group (OH) migration, and, probably, ring closure to the cyclic 2-hydroxy-oxaziridine isomer (c-H₂CON(OH)) as well. The importance of hydrogen migrations was also verified via the nitrosomethane (CH₃NO) – formaldehyde oxime isomer (CH₂NOH) pair.