An experimental photochemistry study involving gas-and solid-phase amino acids (glycine, DL-valine, DL-proline) and nucleobases (adenine and uracil) under soft X-rays was performed.The aim was to test the molecular stabilities of essential biomolecules against ionizing photon fields inside dense molecular clouds and protostellar discs analogs. In these environments, the main energy sources are the cosmic rays and soft X-rays. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing 150-eV photons. In situ sample analysis was performed by time-of-flight mass spectrometer (TOF-MS) and Fourier transform infrared (FTIR) spectrometer, for gas-and solid-phase analysis, respectively. The half-life of solid-phase amino acids, assumed to be present at grain mantles, is at least 3 × 10 5 and 3 × 10 8 yr inside dense molecular clouds and protoplanetary discs, respectively. We estimate that for gas-phase compounds these values increase 1 order of magnitude since the dissociation cross-section of glycine is lower in gas phase than in solid phase for the same photon energy. The half-life of solid-phase nucleobases is about 2-3 orders of magnitude longer than found for amino acids. The results indicate that nucleobases are much more resistant to ionizing radiation than amino acids. We consider these implications for the survival and transfer of biomolecules in space environments.

The electronic properties of fluorosulfonyl isocyanate, FSO2NCO, were investigated by means of photoelectron spectroscopy and synchrotron based techniques. The first ionization potential occurs at 12.3 eV and was attributed to the ejection of electrons formally located at the π NCO molecular orbital (MO), with a contribution from nonbonding orbitals at the oxygen atoms of the SO2 group. The proposed interpretation of the photoelectron spectrum is consistent with related molecules reported previously and also with the prediction of OVGF (outer valence green function) and P3 (partial third order) calculations. The energy of the inner- and core-shell electrons was determined using X-ray absorption, measuring the total ion yield spectra, and the resonances before each ionization threshold were interpreted in terms of transitions to vacant molecular orbitals. The ionic fragmentation mechanisms in the valence energy region were studied using time-of-flight mass spectrometry as a function of the energy of the incident radiation. At 13 eV the M(+) was the only ion detected in the photoion-photoelectron-coincidence spectrum, while the FSO2(+) fragment, formed through the breaking of the S-N single bond, appears as the most intense fragment for energies higher than 15 eV. The photoion-photoion-photoelectron-coincidence spectra, taken at the inner- and core-levels energy regions, revealed several different fragmentation pathways, being the most important ones secondary decay after deferred charge separation mechanisms leading to the formation of the O(+)/S(+) and C(+)/O(+) pairs.

Ionic fragmentation of the sublimated amino acid DL-proline has been studied using time-of-flight mass spectrometry and synchrotron radiation. Total ion yield and mass spectra were recorded in the 13 to 21.6 eV energy range. Partial ion yields have been calculated for the produced fragments and the results analyzed in a comparative way. Mass spectrum of proline previously obtained at 21.21 eV using photons from a discharge lamp (He I), was used as reference in the comparison to the synchrotron radiation based spectra. The loss of the COOH fragment represents the most probable dissociation pathway following the photoionization of DLproline in the valence region. These are the fi rst results of total and partial ion yields spectra for this molecule in its gas phase in the valence region using time-of-flight spectrometry.

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In this work, we report a joint experimental-theoretical investigation on interaction of vacuum-ultraviolet radiation with trimethylphosphate (TMP) molecule (C(3)H(9)O(4)P) in gas phase. This species together with tetrahydrofuran (THF) are model compounds of deoxyribose nucleic acids (DNA)/ribose nucleic acids (RNA) backbone. Absolute photoabsorption cross sections (σ(a)) and ionization yields (η) are measured using the double-ion-chamber technique in the 11.0-21.45 eV energy range. Photoionization (σ(i)) and neutral-decay (σ(n)) cross sections in absolute scale are also derived. Moreover, theoretical photoabsorption cross sections are calculated using the time-dependent density functional theory from the excitation threshold up to 16 eV. Good agreement between the present calculated and experimental photoabsorption cross sections in the 11.0-14.5 eV range is encouraging. Also, the present measured data of σ(a) and σ(i) for TMP are about 1.3 and 1.5 times of those of THF, respectively. Thus, the experimental evidences that the majority of strand breaks being located at sugar rings in the irradiated DNA/RNA backbone moiety may be induced by a possible migration of the hole, initially created at phosphate group, to the linked sugar groups. Finally, absolute partial photoionization cross sections are derived from the experimental time-of-flight mass spectra.