Coordinator: Maria Elisabetta Palumbo, INAF - Osservatorio Astrofisico di Catania, Italy

As evidence for the key role of heterogeneous chemistry in astrochemistry becomes increasingly apparent, several key questions have been highlighted:

• To understand the formation of dust in the interstellar medium.
• To understand the formation of simple molecules on model dust grain surfaces.
• To understand the physical processes that result when an icy grain mantle is heated or irradiated with light, electrons or ions.
• To understand the role of these processes on observations of grains, ices and the molecules formed by the intermediary of grains and their icy mantles in the evolving Universe.

New research topics in this area that may be developed by all Working Groups as part of this Action are:

1. Formation of grains, small molecules and ices

   The topic of this research theme is to study the formation of dust grains and their optical properties, the formation of small molecules on grains, and the reactive accretion of icy layers and the morphological and spectroscopic properties of the resulting icy films. In particular to develop studies of:

   • The mechanism of formation of interstellar dust grains from their initial condensation through to grain aggregate formation via grain-grain collisions.
   • The release of reaction energy in the heterogeneous formation of small molecules on model dust grain surfaces leading to molecular products with high degree of internal (rotational/vibrational energy).
   • The rates of ice formation on model dust grain surfaces.
   • The morphology of ices formed on model dust grain surfaces.
   • The infrared, optical and ultraviolet spectroscopy of ices formed on model dust grain surfaces.
2. Physical processes in and on icy grains.

   The primary aim in this theme is to develop a comprehensive understanding of the physical processes occurring when an icy mantle is subjected to electromagnetic radiation or bombarded with charged and/or neutral particles. Studies in this part of the scientific programme of the Action should focus on:

   • Understanding the thermal desorption of both simple ices, complex mixed ices and clathrates as may be observed in the cold, dense regions of the ISM associated with star formation.
   • Understanding desorption of both simples ices, complex mixed ices and clathrates induced through interaction with electromagnetic radiation from the IR to the soft X-ray.
   • Understanding desorption of both simple ices, complex mixed ices and clathrates induced through interaction with low energy electrons and models of cosmic rays.
   • Understanding the role of heat, electromagnetic radiation from the IR to the soft X-ray, and cosmic rays in promoting changes in morphology in icy films.
3. Chemical transformations in and on icy grains.

   The topic of research theme 3 is to study the evolution and to simulate the formation of complex molecules of astrophysical interest on grains and in interstellar ices under laboratory controlled conditions with an unprecedented level of detail and sensitivity. This will require collaboration between astrochemists and surface scientists. The focus will be on:

   • Ultraviolet (UV) photon- and low energy electron-induced chemical transformations.
   • Vacuum UV radiation, extreme UV radiation, and X-ray photon- and cosmic ray induced chemical transformations.
   • Chemical transformations following atom, radical or thermal molecular ion
   • bombardment, using for instance special thermal cracking and microwave discharge sources.
4. Modelling the gas-grain interaction.

   Computational and simulation research should closely follow the empirical goals of themes 1 through 3 and focus on:

   • Developing models for amorphous ices.
   • Calculated IR and UV absorption spectra for water and adsorbates on and in crystalline and amorphous ices.
   • Understanding the dynamics of photon-driven processes in amorphous ices, including photodesorption and photodissociation.
   • Understanding molecular hydrogen formation on graphite and amorphous ice.
   • Understanding the hydrogenation reactions of CO in various types of ice, particularly CH3OH formation.
   • Simulating diffusion of hydrogen atoms and oxygen atoms on hexagonal, cubic and amorphous ices.
   • Simulating the condensation and growth of grains.
   • Simulating the growth and evolution of water ice and other solids of relevant small molecules under interstellar conditions.
5. Observations and astronomical models involving dust and ices.

   The primary goal of this theme is to obtain quantitative astronomical constraints on the role of grains in interstellar chemistry. This requires a combination of observations and modelling. This may include:

   • Large and small scale maps of infrared lines of H₂ and deuterated species may be constructed to trace its formation on grain surfaces under different conditions.
   • The assembly of an inventory of ices in different environments (temperature, density, UV) using infrared spectroscopy, e. g. the Spitzer Space Telescope.
   • Search for the ultimate molecular complexity in space by radio, sub-millimeter and far- IR (Herschel) unbiased spectral surveys observations.
   • A determination of the formation and lifecycle of water from gas to solid and back again by combining infrared spectroscopy of water ice with sub-millimeter spectroscopy of water gas from for example the Herschel Space Observatory.
   • A study of the formation and composition of silicate and carbonaceous grains in disks and envelopes around young and old stars using infrared spectroscopy.
   • Studies with high spatial resolution IR spectroscopy of photon-dominated regions in nebulae and around stars, looking at how the emission band strengths and relative intensities vary with distance from the exciting source as a diagnostic of polycyclic aromatic hydrocarbon formation and excitation mechanisms.
   • Modelling of the gas-grain chemistry in hot cores and disks using the new laboratory data and compare with observations.

To obtain information about the group members, please check the group members webpage.

If you would like to join this working group, please contact the coordinator M. E. Palumbo, INAF - Osservatorio Astrofisico di Catania, Italy, phone: ++39-0957332242, e-mail: mepalumbo [at] oact [dot] inaf [dot] it