Isoviolanthrene (C34H18), a polycyclic aromatic hydrocarbon (PAH) molecule, was studied via matrix isolation in argon and water at 20 K. Infrared spectroscopy was performed in situ where samples were irradiated using ultraviolet light. Experimental spectra were compared to theoretical spectra for vibrational band assignment, determination of the corresponding A-values, and photoproduct identification. Isoviolanthrene was also deposited as a thin film and irradiated with different energy sources: ultraviolet photons (10.2 eV), soft electrons (1.5 keV), protons (1.5 MeV), and He+ particles (1.5 MeV), to understand the effects of different energy sources on a PAH. Anions and cations of isoviolanthrene were produced as a result of UV photolysis in an argon matrix. Hydrogen- and oxygen-rich aromatic photoproducts were produced by ultraviolet photons when isoviolanthrene was isolated in a water matrix. The irradiated PAH thin films results were dependent on the energy source. Irradiation with ultraviolet photons yielded a broad underlying feature centered at 9.6 μm, while bombardment with soft electrons gave a broad feature centered at 7.7 μm. In the case of proton bombardment, no broad feature was detected, in contrast with He+ bombardment that destroyed most of the isoviolanthrene and produced broad features in the C-Hoop and C–H stretching regions. A comparison of astronomical IR emission observations with our experimental results in the mid-infrared range has revealed a similarity between the observed plateaus and the broad features produced by our experiments.

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Radiolysis of biomolecules by fast ions has interest in medical applications and astrobiology. The radiolysis of solid D-valine (0.2–2 μm thick) was performed at room temperature by 1.5 MeV H+, He+, N+, and 230 MeV S15+ ion beams. The samples were prepared by spraying/dropping valine-water-ethanol solution on ZnSe substrate. Radiolysis was monitored by infrared spectroscopy (FTIR) through the evolution of the intensity of the valine infrared 2900, 1329, 1271, 948, and 716 cm−1 bands as a function of projectile fluence. At the end of sample irradiation, residues (tholins) presenting a brownish color are observed. The dependence of the apparent (sputtering + radiolysis) destruction cross section, σd, on the beam stopping power in valine is found to follow the power law σd = aSen, with n close to 1. Thus, σd is approximately proportional to the absorbed dose. Destruction rates due to the main galactic cosmic ray species are calculated, yielding a million year half-life for solid valine in space. Data obtained in this work aim a better understanding on the radioresistance of complex organic molecules and formation of radioproducts.

Degradation of L-valine by 0.06 - 1.0 keV electron beams is analysed in laboratory, at 10, 150 and 300 K. Valine film thicknesses are measured by profilometry, permitting band strength determination for selected valine bands. The column density evolutions during the irradiation are measured via infrared spectroscopy and destruction cross sections are extracted; they range from 1 – 100 × 10−16 cm2. Data show that, in general, destruction cross sections depend not only on projectile energy and sample temperature but also on sample thickness and beam fluence. In order to understand these findings, a statistical model is proposed for describing the radiolysis of organic materials. Comparing predictions with experimental results for valine, the main trends are reproduced. The quantitative disagreement indicates that it is necessary to include sputtering in the model. A major contribution of the model is to permit to simulate, layer by layer, the sample degradation rate as a function of fluence. The model assumes that the destruction cross section of precursor molecules is proportional to the local stopping power and uses the Monte Carlo CASINO code to determine the deposited energy distribution in the bulk. As astrophysical implications, the radiolysis of valine dissolved in H2O ice and shielded by a CO2 layer is predicted, as an attempt to analyse the degradation of realistic cosmic materials by keV electrons.

The amino acid L-valine is analyzed by Fourier Transform InfraRed Spectroscopy (FTIR) in the 40–300 K temperature range. A valine sample was deposited onto a ZnSe substrate, cooled down to 40 K and warmed up back to 300 K, annealed at 120°C for 12 h, cooled down to 40 K and warmed up again to 300 K. FTIR spectra were acquired in transmission mode during this thermal excursion. It was observed that: (i) no phase transition has occurred; (ii) as temperature decreases, the band absorbances increase linearly and the band widths become narrower; (iii) compared to 300 K values, the integrate absorbances (peak areas) at 40 K are 40–100% higher and bandwidths are about half; (iv) the FTIR spectrum behaviors of the annealed and non-annealed samples are similar. The sample is considered to be constituted only by valine zwitterions; bandwidth decrease is explained partially by Doppler effect; absorbance enhancement at low temperatures is caused by stronger Van der Walls forces. These general conclusions are expected to be similar for other amino acids.