Photochemistry of HNCO in Solid Xe:  Channels of UV Photolysis and Creation of H₂NCO Radicals

Abstract

Photolysis of HNCO at wavelengths between 266 and 193 nm is studied in solid Xe with FTIR and laserinduced fluorescence methods. The channels HNCO f H + NCO (a) and HNCO f NH + CO (b) are operative in a Xe matrix. Channel b produces both isolated fragments and NH‚‚‚CO complexes as characterized by the CO absorption. The MP2/6-311++G(3df,3pd) calculations are presented for the NH-CO complexes and compared with the experimental data. Photolysis of NCO produces mainly NO + C. A part of the carbon atoms form C 2 after which C 2 -is created in a photoinduced charge transfer reaction. For comparison, in solid Kr, photolysis of HNCO produces additionally HOCN but this channel is absent in a Xe matrix. Upon annealing of the partially photolyzed matrix at 50 K, hydrogen atoms are mobilized and a radical H 2 NCO is formed by a reaction of a hydrogen atom with a HNCO molecule. Four IR absorptions of H 2 NCO are observed and they agree well with the MP2/6-311++G(3df,3pd) calculations. The assignment is supported by experiments with DNCO. The threshold for the photodecomposition of H 2 NCO is between 365 and 405 nm.

MECHANISTICAL STUDIES ON THE PRODUCTION OF FORMAMIDE (H2NCHO) WITHIN INTERSTELLAR ICE ANALOGS

“…(A color version of this figure is available in the online journal.) consistent with the previously reported matrix-isolated values of 1856 and 1858 cm −1 in xenon (Maier & Lautz 1998;Pettersson et al 1999), 1863 cm −1 in argon (Milligan & Jacox 1969), 1861 cm −1 in carbon monoxide (Ewing et al 1960), and 1853 cm −1 for a 1:1 ratio of carbon monoxide to methane irradiated ice (Bennett et al 2005). For the same ratio of ices where the HCO band was identified, a shoulder consisting of ∼1840 cm −1 was observed.…”

Efficient surface formation route of interstellar hydroxylamine through NO hydrogenation. II. The multilayer regime in interstellar relevant ices

“…4, NCO radicals, NC − and NCO − anions as well as their hydrogenated analogues HNC and HNCO (Refs. [41][42][43][44] are not present in any of our RAIR spectra. Another main result here is that NH 2 OH is not formed upon UV photolysis of water rich ices.…”

Tentative identification of urea and formamide in ISO-SWS infrared spectra of interstellar ices

“…2a) (Allamandola et al 1988) suggests that formaldehyde is produced according to the successive hydrogenation reactions CO + H˙→ HCO˙and HCO˙+ H→ H 2 CO. Formamide formation can be explained by the following reactions H˙+ HNCO → NH 2 CO˙and H˙+ NH 2 CO˙→ HCONH 2 involving the NH 2 CO˙radical as a transient species. This radical has been detected in matrix isolation experiments (Pettersson et al 1999). Finally, we assume that urea formation can result from a recombination between NH 2 CO˙and NH˙2 radicals formed in the prior reactions.…”