Abstract. Laboratory experiments involving vacuum ultraviolet (VUV) irradiation of solid isocyanic acid (HNCO) at 10 K, followed by infrared spectroscopy (FTIR), are used to interpret the complex spectra associated with Interstellar Medium (ISM) dust grains, particularly the spectra associated with the icy phase observed toward dense molecular clouds. The comparison of the infrared spectra of the photolysis products with spectra recorded from the protostellar source NGC 7538 IRS9 shows that the "unexplained" 1700 cm −1 feature can be attributed to the contribution of several species H 2 CO (formaldehyde), HCONH 2 (formamide) and H 2 NCONH 2 (urea) mixed with H 2 O as the main contributor. Urea, formaldehyde and NH− (ammonium cyanate) may also contribute to a band at 1470 cm −1 , widely observed in many protostellar infrared sources and which remains up to now poorly explained in numerous ISO-SWS spectra. Isocyanic acid could be a precursor of formamide and urea in interstellar ices.

No abstract

We report on a study of adsorption of probe molecules on the aluminum sites of γ-alumina surface planes. DFT electronic structure and total energy calculations for ( 100) and (110D) surface planes were carried out in order to find the reactive sites. The adsorption of two molecular species (water and hydrogen sulfide) was studied using a DFT plane-wave pseudopotential method. We found that both molecules were adsorbed on the (100) surface and that both molecules were dissociated on the (110D) surface. Consequently, the (110D) surface is more reactive than the (100) surface.

The UV isomerization of formamide (HCONH2) trapped in xenon, nitrogen, argon, and neon cryogenic matrices has been monitored by Fourier transform infrared (FT-IR) spectroscopy. Formamide monomer is the only species present in the matrices after deposition; when UV-selective irradiation was carried out at 240 nm, the n --> pi transition allowed us to observe the formation of several isomers of formimidic acid [H(OH)C=NH]. On these latter species, we carried out selective IR irradiation of their OH stretching mode and compared the experimental and theoretical (B3LYP/6-311+G(2d,2p)) sets of bands. This study allowed us to characterize for the first time all the isomers of formimidic acid. We have then studied the vacuum UV photodecomposition (lambda > 160 nm) of this molecule at 10 K in argon and xenon matrices. Several primary photoproducts such as HCN.H2O, HNC.H2O, and HNCO.H2 complexes, yielded by dehydration and dehydrogenation processes, were characterized.