Importance of backdonation in [M–(CO)]p+ complexes isoelectronic to [Au–(CO)]+

International audienc

Adsorption of atomic hydrogen as driving vector for solid-gas processes on ices

International audienceA consensus has progressively developed that the path towards complex organic molecules could be favoured by the icy mantles of interstellar dust particles. However, the question of whether activation energy is required to promote those reactions is open. This work deals with the simplest process thought to increase complexity i.e. successive additions of a single atom (H). Two situations can be considered, the direct additions of H in the gas phase and the atomic hydrogenation processes on water ice surfaces available in the interstellar medium (ISM). The synthesis of methanol, largely discussed in the literature is revisited as a case study. Computational investigations of the reactions leading from CO to CH3OH show that, with [H...(H2O)n] complexes as hydrogenation vectors, all steps of the process are barrier-less, contrary to the gas phase process and this, whatever the level of theory considered. The key parameter is the position of the CO + [H...(H2O)n] initial system on the global energy scale. At the present level of theory, when H is pre-adsorbed on the ice, the system happens to be high enough above the reaction path, namely, above any intermediates and possible transition states. This is true whatever the dimension of the ice support, even for the simplest model of one H2O molecule. Application of such a simplified synthetic approach, here validated for the synthesis of methanol, could be generalized, providing a simple way to get a fair insight into the important class of atomic hydrogenations on ices in the ISM

Trends in ns2np0 [M(CO)]q+ complexes: From germanium to element 114 (Uuq)

International audienc

Enforcing hemidirectionality in Pb(II) complexes: The importance of anionic ligands

International audienc

Lead Substitution in Synaptotagmin: A Case Study

International audienc

Design Of Next Generation Force Fields From AB Initio Computations: Beyond Point Charges Electrostatics

International audienc

Design Of Next Generation Force Fields From AB Initio Computations: Beyond Point Charges Electrostatics

International audienc

Search for hydrogen-helium molecular species in space

International audienceContext. Helium, the second most abundant element in the Universe, with a relative abundance of He/H ~ 1/10, has never been observed in any other form than that of a neutral atom (He) or an ion (He+) in the interstellar medium. Since He is a noble gas its non-observation as part of neutral molecular systems is understandable, but it is very surprising for a positively charged species such as HeH+ that is a stable diatomic ion whose spectral signatures are well known in the laboratory. Aims. This non-observation, even in hydrogen rich regions, could imply that HeH+ is not a proper target and that alternatives have to be considered, such as small HeHn+ clusters. The present study aims at finding whether the leading term HeH3+ fulfills the conditions required.Methods. We addressed the question with state-of-the-art numerical simulations. We determined a two-dimension ab initio potential energy surface (PES) of the HeH3+ cluster along the He...H3+ and HeH+...H2 reaction coordinates. The calculations rely on complete active space configuration interaction followed by a second order perturbation treatment (CAS-PT2). This surface was used for the evaluation of the two radiative associations rate constants by means of a quantum treatment of the collision between the interacting fragments. Results. These calculations show unambiguously that HeH3+ is the most stable point on the corresponding global PES. Then, we determined the rate constants of the radiative associations HeH+ + H2 and He + H3+ leading to HeH3+. Conclusions. Significative values were obtained that reach up to 2 × 10-18 cm3 s-1, which should stimulate new tentatives to detect molecular helium in astrophysical objects