The interpretation of molecular line surveys at millimetre and submillimetre wavelengths towards astrophysical objects requires a good knowledge of the spectroscopy of the molecules present in the gas phase, and of the basic collisional processes between them and molecular and atomic Hydrogen, Helium, and electrons. From the chemical point of view, the modeling of these data requires a large amount of laboratory information concerning the reactivity of these species in the gas phase and in the ice mantles of dust grains. In this contribution I will focus on the problems to interpret line surveys and I will discuss how we will have to proceed in the new era opened by ALMA where sensitivity and angular resolution will surpass by nearly a factor 10 those of existing facilities, and where the spectral confusion limit could be reached towards many sources.

Laboratory analysis of spectra of potential interstellar molecules from the radio-frequency to the THz range is a prerequisite for their subsequent identification by radioastronomical techniques. The spectral analysis allows us to derive molecular parameters that are able to model the frequency and intensity patterns of the transitions, as well as to predict with a high degree of precision the frequencies of transitions not measured in the laboratory.

Our laboratories have recently calculated a set of collision coefficients characterizing the efficiency of energy transfer between helium and/or hydrogen and a large variety of interstellar molecules. We have considered with molecules ranging from light hydrides, observed by the Herschel Space Observatory, to medium size molecules, observed by mm antennas, to heavy complex organic molecules, observed also in the cm range. We present a review of recent theoretical results obtained in our laboratories, for various kinds of commonly observed molecules.

Modeling of molecular emission from interstellar clouds requires the calculation of rate coefficients for excitation by collision with the most abundant species. Based on new highly correlated potential energy surfaces, rotational excitation of C2H and C2H− radicals in collision with He are investigated. C2H fine and hyperfine structure is taken into account. As already found for other systems, rate coefficients for the C2H− ion are larger by a factor up to 3 compared to the neutral species.

It is demonstrated on quantum mechanical grounds that the dissociative recombination of HSCNH+ with an electron, a reaction of interest to the chemistry of molecular interstellar clouds, leads either to HSCN or to HNCS. The HSCNH+ cation, thus far undiscovered in space, is therefore proposed as a precursor for both neutral interstellar species, while H2NCS+ (32 kJ/mol more stable than HSCNH+, according to our quantum-chemical calculations) can yield only HNCS. Calculations of potential energy surfaces were carried out for both cationic precursors.

Both emission and absorption techniques have been developed at the AILES beamline of SOLEIL synchrotron to record far infrared (FIR) spectra of transient species. To illustrate the possibilities offered by our absorption set-up, we report in this paper new rotational transitions of the SO radical falling in the spectral range covered by the HIFI spectrometer onboard Herschel.

More than 100 reactions between stable molecules and free radicals have been shown to remain rapid at low temperatures. In contrast, reactions between two unstable radicals have received much less attention due to the added complexity of producing and measuring excess radical concentrations. We performed kinetic experiments on the barrierless N + OH and N + CN reactions in a supersonic flow (Laval nozzle) reactor. The results provide insight into the gas-phase formation mechanisms of molecular nitrogen in interstellar clouds (ISCs).

KIDA (for KInetic Database for Astrochemistry) is a project initiated by different communities in order to 1) improve the interaction between astrochemists and physico-chemists and 2) simplify the work of modeling the chemistry of astrophysical environments. KIDA was designed to group at the same place and with the same format all gas-phase chemical reactions useful for astrochemical simulations of the interstellar medium and planetary atmospheres. From KIDA, a subset of chemical reactions has been extracted for the cold and dense interstellar medium: kida.uva.2001.

We report a theoretical study of dissociative recombination (DR) of BeH+ by low energy electron impact, using previously computed molecular data as input for a Multichannel Quantum Defect Theory (MQDT) approach. Three electronic symmetries of BeH, 2Π, 2Σ+, and 2Δ have been included in the calculations. We present cross sections and thermal rate coefficients ready to be used in the modelling of the BeH+ abundance in the interstellar medium and stellar atmosphere.

A new experimental setup is described that allows us to study the state-selected photodissociation dynamics of small molecules of astrophysical interest using two independently tunable VUV radiation sources.

For many years, our group has been investigating the VUV spectroscopy and photochemistry of molecules of astrophysical (Jochims et al. 2006a,b; Leach et al. 2008; Schwell et al. 2012) and prebiotic interest (Schwell et al. 2006). Polyynes and cyano-polyynes that are abundant in the interstellar medium (ISM) and in planetary atmospheres, have been investigated too (e.g. Fray et al. 2010). An aerosol source for reactive and thermo-labile compounds has been developed (Gaie-Levrel et al. 2011) to perform gas-phase measurements. These are necessary to measure intrinsic molecular properties and to compare to quantum chemical calculations. Besides measuring absolute absorption and photoionization cross sections, dissociative channels and their involved excited states are identified for a number of molecules of interstellar interest. Branching ratios of the respective elementary photoreactions are determined in order to understand and model the photochemistry occurring in the ISM. Some very recent results on the dissociative photoionization of methylformate (MF), glycolaldehyde (GA), dimethylether (DIM), aminoacetonitrile (AAC) and cyanoacetylene (CA), are presented here.

Numerous hydrogenated molecules observed in comets and the interstellar medium present nuclear spin isomers. The non-thermal ortho: para ratios measured in space are believed to be of high diagnostic value, allowing remote measurement of physical conditions prevailing in the past, such as the initial temperature associated with a molecular formation or condensation. The lack of laboratory studies on interactions at the gas-solid interface limits our current interpretation of observations. Recent progress in nuclear spin conversion (NSC) dynamics are discussed in this paper. Results on water and methane in cryogenic matrices illustrate the conversion mechanisms within the condensed phase at very low temperatures. NSC of molecular hydrogen at the surface of 10 K Amorphous Solid Water (ASW) shows surface mediated conversion processes for molecular hydrogen. NSC involving molecular ices are discussed in the light of few recent studies, including UV photodesorption investigations.

Desorption of condensed species is a key process in controlling the balance of material between the solid and gaseous phases in the interstellar medium. Therefore, a quantitative understanding of desorption in astrophysical environments, by both thermal and non-thermal mechanisms, is essential for development of the field of astrochemistry. This paper briefly reviews recent progress in the study of desorption by experimental and computational methods, and identifies some areas with potential for development in the near future.

Ice desorption affects the evolution of the gas-phase chemistry during the protostellar stage, and also determines the ice composition of comets forming in circumstellar disks. From observations, most volatile species, including CO2, are found in H2O-dominated ices. In this study, the desorption of CO2 mixed in H2O ice and the impact of ice thickness, mixture ratio and heating rate are experimentally determined. The results are used to parametrize an extended three-phase model (gas, ice surface and ice mantle) which describes ice mixture desorption using rate equations and a minimum number of free parameters. The model can be used to predict the evolution in thickness and concentration of volatile-rich H2O ice during infall of icy grains around protostars.

The accretion and desorption processes of gas molecules on cold grains play an important role in the evolution of dense clouds and circumstellar regions around YSOs. Given the low temperatures in dark cloud interiors (10–20 K), thermal desorption is negligible and most molecules are expected to stick to grains leading to depletion in the gas phase. Laboratory simulations of these processes under astrophysically relevant conditions are required for their understanding. The use of ultra-high-vacuum conditions minimalizes contamination by background water accretion. This introduces a radical improvement, allowing the study of photodesorption and the detection of products at very low abundances in a water-free ice matrix. We studied UV-photoprocessing of pure NH3 and N2 ices under ultra-high-vacuum conditions using the Interstellar Astrochemistry Chamber. The photodesorbed molecules, and the volatile products released upon photolysis and warm-up, were detected in situ by quadrupole mass spectroscopy.

We have developed a new laboratory approach to investigate the evolution of interstellar ices by separating thermal processing from VUV processing. Infrared spectroscopy and mass spectrometry are used to monitor the thermal evolution of ice containing formaldehyde (H2CO) and ammonia (NH3). The main idea is to distinguish photon-induced chemistry from thermally induced chemistry. We show that H2CO and NH3 thermally react at low temperature (40 K) to give aminomethanol (NH2CH2OH). We also show that in presence of HCOOH the warming of an ice mixture H2CO:NH3 gives at room temperature hexamethylenetetramine (HMT-C6H12N4). From an astrobiological point of view, HMT is of significant interest, since its hydrolysis leads to the formation of amino-acids. Furthermore, it is one of the main refractory products obtained after VUV photolysis at 10 K of ice mixtures containing CH3OH and NH3. It is also suspected to be a part of the organic matter present in comets and asteroids. In this contribution, we demonstrate that HMT can no longer be considered as a reliable indicator of VUV photolysis of ice, as we demonstrate that it can be formed from a purely thermal reaction.

Interstellar ices are widely observed in the infrared spectra of regions where stars and planetary systems form. Photochemical and thermal evolution of these ices is simulated and studied in our laboratory where the resulting production of complex organic residues is routinely performed. Observations of their variability with slightly different starting chemical conditions can be performed by means of infrared spectroscopy. Organic residues have interesting chemical properties that make them good potential candidates for prebiotic chemistry. Numerous other analytical methods (GC-MS, HPLC, mass spectrometry, etc.) can be combined to refine the knowledge of their chemical composition and structure. We present here some results on the obtained organic residue resulting from subsequent heating and sublimation of the irradiated ices which show the formation of some macromolecular species.

We present a combined theoretical and experimental study of the adsorption of two pairs of organic isomers, (i) acetic acid AA (CH3COOH) and methyl formate MF (HCOOCH3), and (ii) ethanol EtOH (CH3CH2OH) and dimethyl ether DME (CH3OCH3), onto crystalline water ice surfaces at low temperatures. Both approaches show that, for each pair, the most stable isomer from a thermodynamical point of view, i.e. AA and EtOH, is also the one which is the more tightly bound to the water ice surface compared to the less stable isomers (MF and DME). This finding, which can be explained by the ability of AA or EtOH to efficiently interact with the ice surface via hydrogen bondings, may have important consequences in an astrophysical context, since it could explain why the most stable isomer is not the most abundant observed in the interstellar gas phase.

The formation of CO2 in quiescent molecular cores has long been of interest to astrochemists as CO2 is one of the most abundant solid phase molecules present in the interstellar medium. Previous studies have concentrated, for the most part, on formation mechanisms involving high energy particle or UV bombardment of ices, to mimic the influence of cosmic rays on solid phase species in the outer, lower density regions of molecular clouds. However, condensed phase CO2 is also observed in the inner, denser regions of clouds, where less UV radiation penetrates. To date, very few studies have been made of CO2 formation in the absence of energetic particles.

Low-energy routes to the formation of CO2 are crucial to explain the high abundances of this molecule observed in quiescent regions. We discuss recent experimental results of a study of the low-energy reaction CO + OH. A simple model, developed to describe the kinetics of the system, suggests that the various reactions of the OH radical are key in characterising the production of CO2 and other species. Our results indicate that some CO2 forms concurrently with H2O in molecular clouds, in line with both previous observations and theory. The results of this research are published in Noble et al. (2011).

Interstellar water ice is mainly amorphous, but the nature of its morphology still remains poorly known. The experimental study described in this work focuses on how relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent recombination. We show that there is an exponential decrease in the porosity of the amorphous water ice sample following hydrogen-atom irradiation. These and other laboratory results lead us to suggest that water ice in space is almost certainly amorphous and non-porous (compact).