We explore experimentally the formation of water molecules from O2 and D atoms on bare grains composed of amorphous silicates analogous to those in diffuse interstellar clouds. We provide the fractions of D2O and D2O2 molecules formed on the silicate surface held at 10 K from the O2 + D pathway using RAIRS and TPD techniques. For comparison, we also study the formation of water molecules on surfaces covered with amorphous water ice representing the dense clouds.

Understanding the chemistry of the interstellar medium necessitates the use of gas-grain chemistry codes along with extensive databases of gas-phase and solid-phase reactions. If reaction rates have been measured for various types of gas phase reactions, no experimental kinetic studies are available for determining solid-state thermal reaction rates. We present here an experimental kinetic study of few purely thermal low-temperature solid-state reactions relevant to interstellar ice chemistry.

We have produced synthetic analogues of cosmic silicates using the Sol Gel method, producing amorphous silicates of composition Mg(x)Ca(1−x)SiO3. Using synchrotron X-ray powder diffraction on Beamline I11 at the Diamond Light Source, together with a newly-commissioned gas cell, real-time powder diffraction scans have been taken of a range of silicates exposed to CO2 under non-ambient conditions. The SXPD is complemented by other techniques including Raman and Infrared Spectroscopy and SEM imaging.

An experiment designed for measuring the electronic spectra of PAH cations and PAH cluster cations has been set up, which is briefly described. The photodissociation spectra, reflecting the absorption spectra, of 2-methyl-naphthalene dimer cation have been recorded in the spectral ranges corresponding to the transitions from the ground state to both the excited charge resonance state and the first allowed local electronic excitation state.

The infrared fluorescence decay and the dispersed emission spectrum are presented for gaseous benzene following 193 nm laser excitation. They were measured with FIREFLY (Fluorescence in the InfraRed from Excited FLYing molecules), a new home-made spectrometer. Redshift and redtail in the CH stretch emission spectra (3.3 μm region) demonstrate that anharmonicity plays a key role when dealing with high internal energies, as it is the case in the interstellar medium.

Dust grains evolve during their lifetime. The chemical and physical composition of grains is determined by processes such as exposure to heat, shocks, gas, UV photons and cosmic rays. The degree of processing varies with the environments, determining different grain properties in different regions of space. In the case of organics, laboratory studies have provided a unifying interpretation of how they appear in the main phases of their evolution in space.

Hydrogenated amorphous carbons (HACs) are considered as laboratory analogues to cosmic carbonaceous nanoparticles in the interstellar medium (ISM). The optical properties of nano-sized HACs may be influenced by the UV processing. The variation of the internal structure leads to dramatic changes in the spectral properties in the FUV-VIS range. This scenario can explain some astronomical features such as the interstellar UV bump at 4.6 μm-1. The spectrum of HACs, irradiated by a dose of UV irradiation that corresponds to 21–33% of the average dose of the UV radiation in diffuse ISM, exhibits a new band centered at 4.6 μm-1. This result confirms, for the first time, the suggestion by Mennella et al. (1996) that irradiated HACs might be considered as the carriers of the interstellar UV bump at 4.6 μm-1. However, the amount of carbon needed to reproduce this band is higher than that available for interstellar carbon dust grains. So the ideal structure of irradiated HACs that would produce a band of sufficient strength has still to be searched for.

Hydrogenated amorphous carbons, an important component of the interstellar carbonaceous dust, possess infrared spectral signatures (at 3.4, 6.9 and 7.3 μm) that are ubiquitous in the diffuse interstellar medium of galaxies, but not observed in dense clouds. To better understand the role played by cosmic rays in the disappearance of these absorption bands, irradiation experiments of hydrocarbon dust analogues have been performed with different swift ions. The results obtained through the in situ infrared monitoring of the samples during the irradiations allow to infer the dehydrogenation effect of the cosmic ray distribution on the interstellar hydrogenated amorphous carbons. The importance of this interstellar dust destruction by cosmic rays is discussed in comparison to other energetic processes in different interstellar environments.

Carbonaceous cosmic dust is mainly observed through infrared spectroscopy either in absorption or in emission. Laboratory soot analogues of this interstellar or circumstellar dust were produced in fuel-rich, low-pressure, premixed and flat, flames. The particles were investigated by infrared absorption spectroscopy in the 2–15 μm spectral region. The details of the spectral features shed some light on the structure of the material and enable the study of its life cycle. In particular, the 8 μm band position is tentatively attributed to defects at the edge or in the polyaromatic units of the materials, revealing these structural changes in astrophysical dust.

We present here the latest results from experimental studies aiming at measuring the Mass Absorption Coefficient (MAC) of interstellar silicate dust analogues at low temperatures in the far infrared and submillimetre domains which are necessary for the analysis of astronomical data. These results show that above 100 μm, the MAC of amorphous silicate nano-grains has a complex dependence with the grain temperature and with the wavelength. This has to be considered when interpreting astronomical observations to avoid errors on the derived parameters such as the dust mass and its physical and chemical properties.

The dust in protoplanetary disks is influenced by many different processes. Among others, heating processes are the most important ones: they change not only the physical and chemical properties of dust particles, but also their emission spectra. In order to compare observed infrared spectra of young stellar systems with laboratory data of hot (up to 655°C) circumstellar dust analogues, we investigate materials, which are important constituents of dust in protoplanetary disks. We calculated the optical constants by means of a simple Lorentzian oscillator fit and applied them to simulations of small-particle emission spectra in order to compare our results with real astronomical spectra of AGB-stars and protoplanetary disks.