Search

The absorption spectrum of ethyne, C2H2, in solid Ar was measured in the wavelength region 107-220 nm with light from a synchrotron. Based on that absorption, irradiation of samples of ethyne dispersed in neon with vacuum-ultraviolet (VUV) radiation yielded various products that were identified through their infrared absorption spectra including C n (n = 3-12), C2H, C2H3, C4H, C4H2, C8H–, and C8H2. The efficiency of photolysis of ethyne and the nature of photoproducts depend on the selected wavelength of VUV light. Information about the photodissociation of C2H2 with various photon energies and the formation and identification of large carbon clusters and hydrides at low temperature might be useful in photochemical models to simulate the composition of the atmosphere of Titan and as a source of aerosols.

Photolysis of methane dispersed (1/1000) in solid Ne at 3 K with vacuum-ultraviolet light from a synchrotron produced infrared absorption lines of several products, including new lines at 3319.3 and 1955.5 cm–1. Based on experiments with isotopic labeling and results of quantum-chemical calculations, these lines are assigned to the C-H stretching and C=C stretching modes, respectively, of interstellar molecule linear C5H radicals.

Chemical reactions of C2H4 dispersed in solid nitrogen at 10 K that occur upon irradiation with Lyα light at a wavelength of 121.6 nm and 500 eV electrons were investigated by measuring the infrared absorption spectra. Photolysis of the matrix samples with 121.6 nm light yielded products, including C2H2, CN, and isomers of C2N2, as well as a pair of HCN and HNC. In contrast, electron bombardment of similar matrix samples mainly resulted in the generation of N3, C2H2, C2H3, C3H2, and C3N−. Mechanisms of the reactions that occur during the photolysis and electron-radiation of the matrix samples are discussed. The results of the study provide insights into the formation of HNC and HCN, as well as nitriles, in N2-rich ice samples containing a small proportion of C2H4.

Electron bombardment of gaseous N2 produces N2 + and N3, which are subsequently trapped in the N2 matrix at 10 K. Both the infrared and ultraviolet absorption spectra of the matrix sample at various stages of electron irradiation were recorded. Apart from a progression observed below 192 nm, with intervals ~900 cm–1, corresponding to the transition of D 2 Π g ← X 2 Σ g + of N2 +, three new progressions were recorded in the range 225-192 nm, with intervals ~1000 cm–1, that correlated well with variations in intensities of the electronic absorption band of N3 at 272.7 nm; an absorption coefficient of 3.76 × 10–17 cm molecule–1 for the transition A 2Σu +← X 2Πg of N3 was estimated for the first time. These newly observed progressions were characterized and the vertical excitation energy and oscillator strength were calculated using time-dependent, density-functional theory. This was based on assigning the three progressions to electronic transitions of N3 from the ground state to 2 2Πu, 1 2Σg +, and 1 2Σg –, respectively.

The infrared (IR) and ultraviolet (UV) absorption spectra of pure solid N2 and CH4 diluted in solid N2 (1/100) irradiated with energetic electrons at 10 K were obtained. The IR absorption measurements of the electron-bombarded pure N2 solid reveal the formation of N3 and N3 +, which was confirmed by the observed electronic transitions A 2Σu +← X 2Πg of N3 and A 3Πu ← X 3Σg – of N3 +. In the case of N2 ice containing a small proportion of CH4, we have identified the products of irradiated CH4/N2 ice, including N3, C n N (n = 1-3), CN2, (CN)2, CH3N, HCN2, HC2N, C(NH)2, HNC, HCN, CH3, C2H, C2H2, CN–, NH3 +, and HC3N+. UV absorption measurement of the ice sample was carried out and the possible carriers associated with the observed absorption bands were assigned and discussed.