IRRADIATION OF ETHYLENE DILUTED IN SOLID NITROGEN WITH VACUUM ULTRAVIOLET LIGHT AND ELECTRONS: ITS IMPLICATIONS FOR THE FORMATION OF HCN AND HNC

Direct evidence for a radiation-induced synthesis of acetonitrile and isoacetonitrile from a 1 : 1 CH4HCN complex at cryogenic temperatures: is it a missing link between inorganic and prebiotic astrochemistry?

Nitriles are important constituents of extraterrestrial media. Nitriles are supposed to play a crucial role in prebiotic chemistry occurring in the interstellar medium. In this work, we have investigated the low-temperature radiation-induced transformations of a 1 : 1 CH₄HCN complex as a plausible precursor of the simplest nitriles using the matrix isolation approach with FTIR spectroscopic detection. The parent complexes isolated in a noble gas (Ng) matrix were obtained by deposition of the CH₄/HCN/Ng gaseous mixture and characterized by comparison of experimental complexation-induced shifts of the HCN fundamentals with the results of the ab initio calculations. It was found that the X-ray irradiation of low-temperature matrices containing the isolated 1 : 1 CH₄HCN complex resulted in the formation of acetonitrile (CH₃CN) and isoacetonitrile (CH₃NC) and it appears to be the first experimental evidence for the formation of C₂ nitriles (acetonitrile and isoacetonitrile) from such a "building block". Additionally, a 1 : 1 CH₄HNC complex was tentatively assigned to the irradiated Ar and Kr matrices. It is demonstrated that the matrix has a strong effect on the CH₃CN/CH₃NC yield ratio, which dramatically increases in the row Ar < Kr < Xe. Also, the efficiency of the radiation-induced formation of the CH₄HNC complex was shown to decrease from Ar to Kr. It is believed that the proposed pathway for acetonitrile formation may be a significant step in the radiation-induced evolution leading to complex organic molecules and biomolecules under astrochemical conditions. Furthermore, the obtained results provide a prominent example of the impact of very weak intermolecular interactions on the radiation-induced transformations in cold media.

Hydrogen-Atom Tunneling in Metaphosphorous Acid

Metaphosphorous acid (HOPO), a key intermediate in phosphorus chemistry, has been generated in syn- and anti-conformations in the gas phase by high-vacuum flash pyrolysis (HVFP) of a molecular precursor ethoxyphosphinidene oxide (EtOPO→C₂ H₄ +HOPO) at ca. 1000 K and subsequently trapped in an N₂ -matrix at 2.8 K. Unlike the two conformers of the nitrogen analogue HONO, the anti-conformer of HOPO undergoes spontaneous rotamerization at 2.8 K via hydrogen-atom tunneling (HAT) with noticeable kinetic isotope effects for H/D (>10⁴ for DOPO) and ¹⁶ O/¹⁸ O (1.19 for H¹⁸ OPO and 1.06 for HOP¹⁸ O) in N₂ -matrices.

Compaction and Destruction Cross-Sections for α-Glycine from Radiolysis Process via 1.0 keV Electron Beam as a Function of Temperature

Glycine is an amino acid that has already been detected in space. It is relevant to estimate its resistance under cosmic radiation. In this way, a sublimate of glycine in α-form on KBr substrate was exposed in the laboratory to a 1.0 keV electron beam. The radiolysis study was performed at 40 K, 80 K, and 300 K sample temperatures. These temperatures were chosen to cover characteristics of the outer space environment. The evolution of glycine compaction and degradation was monitored in real time by infrared spectroscopy (Fourier-transform infrared) by investigation in the spectral ranges of 3500-2100, 1650-1200, and 950-750 cm^-1. The compaction cross-section increases as the glycine temperature decreases. The glycine film thickness layer of ∼160 nm was depleted completely after ∼15 min at 300 K under irradiation with ∼1.4 μA beam current on the target, whereas the glycine depletion at 40 K and 80 K occurred after about 4 h under similar conditions. The destruction cross-section at room temperature is found to be (13.8 ± 0.2) × 10^-17 cm², that is, about 20 times higher than the values for glycine depletion at lower temperatures (<80 K). Emerging and vanishing peak absorbance related to OCN^- and CO bands was observed in 2230-2100 cm^-1 during the radiolysis at 40 K and 80 K. The same new IR bands appear in the range of 1600-1500, 1480-1370, and 1350-1200 cm^-1 after total glycine depletion for all temperature configurations. A strong N-H deformation band growing at 1510 cm^-1 was observed only at 300 K. Finally, the destruction cross-section associated to tholin decay at room temperature is estimated to be (1.30 ± 0.05) × 10^-17 cm². In addition, a correlation between the formation cross-sections for daughter and granddaughter molecules at 300 K is also obtained from the experimental data.

Development of an experimental set-up for low-temperature spectroscopic studies of matrix-isolated molecules and molecular ices using synchrotron radiation

An experimental set-up for studying photophysics and photochemistry of molecules in an inert gas medium (matrix-isolated) and in the ice phase at low temperatures has been developed and commissioned at the Photophysics beamline, Indus-1 synchrotron radiation source. This end-station uses an in-house-developed closed-cycle cryostat for achieving cryo-temperatures (∼10 K). Synchrotron radiation from the Photophysics beamline is used as the source of UV-VUV photons and the system is equipped with a Fourier transform infrared spectrometer for characterization of the molecular species formed at low temperature. Various individual components of the end-station like closed-cycle cryostat, experimental chamber, gas mixing and deposition systems are tested to ascertain that the desired performance criteria are satisfied. The performance of the composite system after integration with the Photophysics beamline is evaluated by recording IR and UV-VUV photoabsorption spectra of sulfur dioxide at low temperatures (10 K), both in the ice phase as well as isolated in argon matrices. Results obtained are in good agreement with earlier literature, thus validating the satisfactory performance of the system. As an off-shoot of the study, the VUV absorption spectrum of matrix-isolated SO₂ in argon matrix up to 10.2 eV is reported here for the first time. This experimental end-station will provide new opportunities to study photon-induced reactions in molecules of environmental, astrochemical and industrial importance. Details of the design, development and initial experimental results obtained are presented.