An Experimental and Theoretical Investigation of the Gas-Phase C(P) + NO Reaction. Low Temperature Rate Constants and Astrochemical Implications.

The reaction between atomic carbon in its ground electronic state, C(P), and nitrous oxide, NO, has been studied below room temperature due to its potential importance for astrochemistry, with both species considered to be present at high abundance levels in a range of interstellar environments. On the experimental side, we measured rate constants for this reaction over the 50-296 K range using a continuous supersonic flow reactor. C(P) atoms were generated by the pulsed photolysis of carbon tetrabromide at 266 nm and were detected by pulsed laser-induced fluorescence at 115.

Gas phase Elemental abundances in Molecular cloudS (GEMS) II. On the quest for the sulphur reservoir in molecular clouds: the HS case.

Context: Sulphur is one of the most abundant elements in the Universe. Surprisingly, sulphuretted molecules are not as abundant as expected in the interstellar medium and the identity of the main sulphur reservoir is still an open question.

Aims: Our goal is to investigate the HS chemistry in dark clouds, as this stable molecule is a potential sulphur reservoir.

Abundances of sulphur molecules in the Horsehead nebula First NS detection in a photodissociation region.

Context: Sulphur is one of the most abundant elements in the Universe (S/H1.310 ) and plays a crucial role in biological systems on Earth. The understanding of its chemistry is therefore of major importance.

Oxygen fractionation in dense molecular clouds.

We have developed the first gas-grain chemical model for oxygen fractionation (also including sulphur fractionation) in dense molecular clouds, demonstrating that gas-phase chemistry generates variable oxygen fractionation levels, with a particularly strong effect for NO, SO, O, and SO. This large effect is due to the efficiency of the neutral O + NO, O + SO, and O + O exchange reactions. The modeling results were compared to new and existing observed isotopic ratios in a selection of cold cores.

First Detection of Interstellar SH.

We present the first detection of gas phase SH in the Horsehead, a moderately UV-irradiated nebula. This confirms the presence of doubly sulfuretted species in the interstellar medium and opens a new challenge for sulfur chemistry. The observed SH abundance is ~5×10, only a factor 4-6 lower than that of the widespread HS molecule.