New kinetic data and product distributions have been obtained using the experimental CRESU technique combined with a theoretical analysis of the reaction mechanism. The astrophysical implications of fast CH3O and CH2OH formation are discussed.

A detailed description of a new ab initio interaction potential energy surfaces for the H2-CO complex computed on a six-dimensional grid (i.e., including the dependence on the H-H and C-O separations) is presented. The interaction energies were first calculated using the coupled-cluster method with single, double, and noniterative triple excitations and large basis sets, followed by an extrapolation procedure. Next, a contribution from iterative triple and noniterative quadruple excitations was added from calculations in smaller basis sets. The resulting interaction energies were then averaged over the ground-state and both ground- and first-excited-states vibrational wave functions of H2 and CO, respectively. The two resulting four-dimensional potential energy surfaces were fitted by analytic expressions. Theoretical infrared spectra calculated from these surfaces have already been shown [P. Jankowski, A. R. W. McKellar, and K. Szalewicz, Science 336, 1147 (2012)] to agree extremely well, to within a few hundredth of wavenumber, with the experimental spectra of the para and orthoH2-CO complex. In the latter case, this agreement enabled an assignment of the experimental spectrum, ten years after it had been measured. In the present paper, we provide details concerning the development of the surfaces and the process of spectral line assignment. Furthermore, we assign some transitions for paraH2-CO that have not been assigned earlier. A completely new element of the present work are experimental investigations of the orthoH2-CO complex using microwave spectroscopy. Vast parts of the measured spectrum have been interpreted by comparisons with the infrared experiments, including new low-temperature ones, and theoretical spectrum. Better understanding of the spectra of both para and orthoH2-CO complexes provides a solid foundation for a new search of the bound H2-CO complex in space.

High resolution microwave and millimeter-wave spectra of HeN-CO clusters with N up to 10, produced in a molecular expansion, were observed. Two series of J = 1-0 transitions were detected, which correspond to the a-type and b-type J = 1-0 transitions of He1-CO. The B rotational constant initially decreases with N and reaches a minimum at N = 3. Its subsequent rise indicates the transition from a molecular complex to a quantum solvated system already for N = 4. For N > or =6, the B value becomes larger than that of He1-CO, indicating an almost free rotation of CO within the helium environment.

Protonation of methane (CH4), a rather rigid molecule well described by quantum mechanics, produces CH5(+), a prototypical floppy molecule that has eluded definitive spectroscopic description. Experimental measurement of high-resolution spectra of pure CH5(+) samples poses a formidable challenge. By applying two types of action spectroscopy predicated on photoinduced reaction with CO2 and photoinhibition of helium cluster growth, we obtained low-temperature, high-resolution spectra of mass-selected CH5(+). On the basis of the very high accuracy of the line positions, we determined a spectrum of combination differences. Analysis of this spectrum enabled derivation of equally accurate ground state-level schemes of the corresponding nuclear spin isomers of CH5(+), as well as tentative quantum number assignment of this enfant terrible of molecular spectroscopy.

Surface chemistry on cosmic dust grains plays an important role in the formation of molecules at low temperatures in the interstellar and circumstellar environments. For the first time, we experimentally put in evidence the catalytic role of dust surfaces using the thermal reaction CO2 + 2NH3 → NH4 + NH2COO -, which is also a proxy of radical-radical reactions. Nanometre-sized amorphous silicate and carbon grains produced in our laboratory were used as grain analogues.Surface catalysis on grains accelerates the kinetics of the reaction studied at a temperature of 80 K by a factor of up to 3 compared to the reaction occurring in the molecular solid. The evidence of the catalytic effect of grain surfaces opens a door for experiments and calculations on the surface formation of interstellar and circumstellar molecules on dust. Ammonium carbamate on the surface of grains or released intact into protostellar or protoplanetary disk phases can give start to a network of prebiotic reactions. Therefore, there should be a great interest to search for ammonium carbamate and its daughter molecule, carbamic acid, in interstellar clouds, protostellar envelopes, and protoplanetary disks.

Understanding the history and evolution of small bodies, such as dust grains and comets, in planet-forming disks is very important to reveal the architectural laws responsible for the creation of planetary systems. These small bodies in cold regions of the disks are typically considered as mixtures of dust particles with molecular ices, where ices cover the surface of a dust core or are actually physically mixed with dust. Whilst the first case, ice-on-dust, has been intensively studied in the laboratory in recent decades, the second case, ice-mixed-withdust, present uncharted territory. This work is the first laboratory study of the temperatureprogrammed desorption (TPD) of water ice mixed with amorphous carbon and silicate grains.We show that the kinetics of desorption of H2O ice depends strongly on the dust/ice mass ratio, probably, due to the desorption of water molecules from a large surface of fractal clusters composed of carbon or silicate grains. In addition, it is shown that water ice molecules are differently bound to silicate grains in contrast to carbon. The results provide a link between the structure and morphology of small cosmic bodies and the kinetics of desorption of water ice included in them.

Whether ice in cold cosmic environments is physically separated from the silicate dust or mixed with individual silicate moieties is not known. However, different grain models give very different compositions and temperatures of grains. The aim of the present study is a comparison of the mid-IR spectra of laboratory silicate-grains/water-ice mixtures with astronomical observations to evaluate the presence of dust/ice mixtures in interstellar and circumstellar environments. The laboratory data can explain the observations assuming reasonable mass-averaged temperatures for the protostellar envelopes and protoplanetary disks demonstrating that a substantial fraction of water ice may be mixed with silicate grains. Based on the combination of laboratory data and infrared observations, we provide evidence of the presence of solid-state water in the diffuse interstellar medium. Our results have implications for future laboratory studies trying to investigate cosmic dust grain analogues and for future observations trying to identify the structure, composition, and temperature of grains in different astrophysical environments.2 Cosmic dust grains with carbonaceous and siliceous composition 1,2 represent the most pristine starting material for planetary systems, influence the thermodynamic properties of the medium by absorption and emission of stellar light, and provide a surface for key astrochemical reactions. Dust grains in cold dense astrophysical environments, such as dense interstellar clouds, protostellar envelopes and planet-forming disks beyond the snow line, are typically considered to be mixtures of dust particles with molecular ices. Water is the main constituent of these ices accounting for more than 60% of the ice in most lines of sight 3 . Ices are believed either to cover the surface of a dust core and/or to be physically mixed with dust. While the first case, ice-on-dust, has been intensively studied in the laboratory in recent decades, the second case, ice-mixed-with-dust, presents practically uncharted territory.The ice-on-dust case is typically modelled by ice mixtures deposited onto standard laboratory substrates, such as gold, copper or KBr, which are not characteristic of cosmic dust grains. In addition to these studies, there are studies on physical-chemical processes, such as formation, desorption, and diffusion of molecules, on the surface of cosmic dust analogues: amorphous carbon grains, atomic carbon foils, graphite, amorphous silica, and amorphous and crystalline silicate grains. The reader can find examples of and references to these experimental studies in recent papers [4][5][6][7][8][9] .Concerning ice-mixed-with-dust, this is a new direction of research started very recently by us [10][11][12] . One of the conclusions of our previous study of the optical constants of dust/ice mixtures 11 was that differences between measured constants and constants calculated using effective medium approaches show that a mathematical mixing (averaging) of the optical constants of water ice and silicates f...

Surface processes on cosmic solids in cold astrophysical environments lead to gas phase depletion and molecular complexity. Most astrophysical models assume that the molecular ice forms a thick multilayer substrate, not interacting with the dust surface. In contrast, we present experimental results demonstrating the importance of the surface for porous grains. We show that cosmic dust grains may be covered by a few monolayers of ice only. This implies that the role of dust surface structure, composition, and reactivity in models describing surface processes in cold interstellar, protostellar, and protoplanetary environments has to be reevaluated.