The dissociation dynamics of n-butylbenzene ions have been measured as a function of the parent ion internal energy. Ions were produced by dispersed synchrotron radiation and energy selected by photoelectron photoion coincidence. The branching ratio of the two fragment ions of mass 91 and 92 was measured over an ion internal energy range from 2 to 6.5 eV. This ratio, which varies from 0.05 to 8.0 is a useful thermometer for the n-butylbenzene ion internal energy. The measured dissociation rates for the production of C7H8+ were modeled with RRKM/QET calculations, from which an activation energy of 0.99 eV was derived. The assumption of a tight transition state with AS = -7 cal/K is necessary in order to account for the slow rise in the dissociation rate with ion internal energy. The small kinetic energy released in the dissociation indicates that the rate-determining step is an isomerization reaction, prior to the actual dissociation.

The discovery of large ( > 100 u) molecules in Titan's upper atmosphere has heightened astrobiological interest in this unique satellite. In particular, complex organic aerosols produced in atmospheres containing C, N, O, and H, like that of Titan, could be a source of prebiotic molecules. In this work, aerosols produced in a Titan atmosphere simulation experiment with enhanced CO (N 2 /CH 4 /CO gas mixtures of 96.2%/2.0%/1.8% and 93.2%/5.0%/ 1.8%) were found to contain 18 molecules with molecular formulae that correspond to biological amino acids and nucleotide bases. Very high-resolution mass spectrometry of isotopically labeled samples confirmed that C 4 H 5 N 3 O, C 4 H 4 N 2 O 2 , C 5 H 6 N 2 O 2 , C 5 H 5 N 5 , and C 6 H 9 N 3 O 2 are produced by chemistry in the simulation chamber. Gas chromatography-mass spectrometry (GC-MS) analyses of the non-isotopic samples confirmed the presence of cytosine (C 4 H 5 N 3 O), uracil (C 5 H 4 N 2 O 2 ), thymine (C 5 H 6 N 2 O 2 ), guanine (C 5 H 5 N 5 O), glycine (C 2 H 5 NO 2 ), and alanine (C 3 H 7 NO 2 ). Adenine (C 5 H 5 N 5 ) was detected by GC-MS in isotopically labeled samples. The remaining prebiotic molecules were detected in unlabeled samples only and may have been affected by contamination in the chamber. These results demonstrate that prebiotic molecules can be formed by the highenergy chemistry similar to that which occurs in planetary upper atmospheres and therefore identifies a new source of prebiotic material, potentially increasing the range of planets where life could begin.

No abstract

In order to separate the fundamental synchrotron radiation from the high harmonics emitted by an undulator, a low photon energy-pass filter has been designed and built, ensuring a high spectral purity on the vacuum ultraviolet (VUV) SU5 beamline at Super-ACO. It consists of an absorption cell filled with rare gases and separated from the ultrahigh vacuum of the storage ring and of the beamline by a double differential pumping obtained with thin capillaries. Its conception has been optimized by numerical computation of pumping speed. Admission pressures in the range of 100 Pa in the central part of the filter have been used without any degradation of the upstream or downstream ultrahigh vacuum. The measured attenuation factors above the energy cutoff are above 105 and 102 (and certainly above 103 with ultimate pressure of Ne) for argon and neon absorbing gases, respectively, with no measurable attenuation of fundamental radiation. A sophisticated numerical simulation of the pressure distribution, taking into account the geometry of the whole absorption cell including the first pair of capillaries, has been developed. The corresponding calculated attenuation factors are in very good agreement with the measurements, and thus allow reliable predictions of the expected attenuation factors for any given configuration of the filter.

Fluorescence excitation spectra of OH(A), OH(B), OH(C), Lyman α, Balmer α, Balmer β, and H2O+(Ã) are recorded in H2O in the 9–35 eV photon excitation range. The OH(A) fluorescence quantum yield is measured from 9.2 to 13.6 eV incident photon energy. The pressure dependence of the H2O+(Ã) fluorescence excitation spectrum is investigated and the quenching rate constant of H2O+(Ã) by H2O is found to be equal to (4±2)×10−10 cm3 s−1. New Rydberg states are observed: a continuum-like state in the 10–12.6 eV range assigned to the (3a1)−1 (3pb2) 1B2 state and two broad bands lying at 27–29 and 30–32 eV, respectively, assigned to Rydberg states converging towards the (2a1)−1 innervalence state of H2O+. The valence character of the nsa1 Rydberg states is discussed. The decay processes of valence-type vs pure Rydberg states are investigated. All energetically accessible dissociation channels producing fluorescent fragments are observed and the fragments appear at their thermodynamical threshold. The competition between autoionization and dissociation into neutrals is shown to occur only for pure Rydberg states. Possible dissociation mechanisms are discussed.

In this work Titan's atmospheric chemistry is simulated using a capacitively coupled plasma radio frequency discharge in a N(2)-CH(4) stationnary flux. Samples of Titan's tholins are produced in gaseous mixtures containing either 2 or 10% methane before the plasma discharge, covering the methane concentration range measured in Titan's atmosphere. We study their solubility and associated morphology, their infrared spectroscopy signature and the mass distribution of the soluble fraction by mass spectrometry. An important result is to highlight that the previous Titan's tholin solubility studies are inappropriate to fully characterize such a heterogeneous organic matter and we develop a new protocol to evaluate quantitatively tholins solubility. We find that tholins contain up to 35% in mass of molecules soluble in methanol, attached to a hardly insoluble fraction. Methanol is then chosen as a discriminating solvent to characterize the differences between soluble and insoluble species constituting the bulk tholins. No significant morphological change of shape or surface feature is derived from scanning electron microscopy after the extraction of the soluble fraction. This observation suggests a solid structure despite an important porosity of the grains. Infrared spectroscopy is recorded for both fractions. The IR spectra of the bulk, soluble, and insoluble tholins fractions are found to be very similar and reveal identical chemical signatures of nitrogen bearing functions and aliphatic groups. This result confirms that the chemical information collected when analyzing only the soluble fraction provides a valuable insight representative of the bulk material. The soluble fraction is ionized with an atmospheric pressure photoionization source and analyzed by a hybrid mass spectrometer. The congested mass spectra with one peak at every mass unit between 50 and 800 u confirm that the soluble fraction contains a complex mixture of organic molecules. The broad distribution, however, exhibits a regular pattern of mass clusters. Tandem collision induced dissociation analysis is performed in the negative ion mode to retrieve structural information. It reveals that (i) the molecules are ended by methyl, amine and cyanide groups, (ii) a 27 u neutral moiety (most probably HCN) is often released in the fragmentation of tholin anions, and (iii) an ubiquitous ionic fragment at m/z 66 is found in all tandem spectra. A tentative structure is proposed for this negative ion.

No abstract

This paper presents a review of the current knowledge on the doubly-charged atomic and molecular positive ions in the planetary atmospheres of the Solar System. It is focused on the terrestrial planets which have a dense atmosphere of N(2) or CO(2), i.e. Venus, the Earth and Mars, but also includes Titan, the largest satellite of Saturn, which has a dense atmosphere composed mainly of N(2) and a few percent of methane. Given the composition of these neutral atmospheres, the following species are considered: C(++), N(++), O(++), CH(4)(++), CO(++), N(2)(++), NO(++), O(2)(++), Ar(++) and CO(2)(++). We first discuss the status of their detection in the atmospheres of planets. Then, we provide a comprehensive review of their complex and original photochemistry, production and loss processes. Synthesis tables are provided for those ions, while a discussion on individual species is also provided. Methods for detecting doubly-charged ions in planetary atmospheres are presented, namely with mass-spectrometry, remote sensing and fine plasma density measurements. A section covers some original applications, like the possible effect of the presence of doubly-charged ions on the escape of an atmosphere, which is a key topic of ongoing planetary exploration, related to the evolution of a planet. The results of models, displayed in a comparative way for Venus, Earth, Mars and Titan, are discussed, as they can predict the presence of doubly-charged ions and will certainly trigger new investigations. Finally we give our view concerning next steps, challenges and needs for future studies, hoping that new scientific results will be achieved in the coming years and feed the necessary interdisciplinary exchanges amongst different scientific communities.