Reaction of H + HONO in solid para-hydrogen: infrared spectrum of ˙ONH(OH).

Abstract

Hydrogenation reactions in the N/O chemical network are important for an understanding of the mechanism of formation of organic molecules in dark interstellar clouds, but many reactions remain unknown. We present the results of the reaction H + HONO in solid para-hydrogen (p-H2) at 3.3 K investigated with infrared spectra. Two methods that produced hydrogen atoms were the irradiation of HONO molecules in p-H2 at 365 nm to produce OH radicals that reacted readily with nearby H2 to produce mobile H atoms, and irradiation of Cl2 molecules (co-deposited with HONO) in p-H2 at 405 nm to produce Cl atoms that reacted, upon IR irradiation of the p-H2 matrix, readily with nearby H2 to produce mobile H atoms. In both experiments, we assigned IR lines at 3549.6 (ν1), 1465.0 (ν3), 1372.2 (ν4), 898.5/895.6 (ν6), and 630.9 (ν7) cm-1 to hydroxy(oxido)-λ5-azanyl radical [˙ONH(OH)], the primary product of HONO hydrogenation. Two weak lines at 3603.4 and 991.0 cm-1 are tentatively assigned to the dihydroxy-λ5-azanyl radical, ˙N(OH)2. The assignments were derived according to the consideration of possible reactions and comparison of observed vibrational wavenumbers and their IR intensities with values predicted quantum-chemically with the B3LYP/aug-cc-pVTZ method. The agreement between observed and calculated D/H- and 15N/14N-isotopic ratios further supports these assignments. The role of this reaction in the N/O chemical network in dark interstellar clouds is discussed.