LASSIE FP7 ITN
LABORATORY ASTROCHEMICAL SURFACE SCIENCE IN EUROPE

SEVENTH FRAMEWORK PROGRAMME    INITIAL TRAINING NETWORKS



Scientific and Technological Objectives of the Research and Training Programme

WP1 - Formation of Grains, Small Molecules and Ices
WP2 - Physical Processes in and on Icy Grains
WP3 - Chemical Transformations in and on Icy Grains
WP4 - Modelling the Gas-Grain Interaction
WP5 - Observations and Astronomical Models Involving Dust and Ices

Research Programme

These research themes stated above form the basic structure of the scientific programme of the LASSIE ITN. Each theme addresses clearly defined scientific aims and objectives that constitute the separate research sub-programmes. These, in turn, will provide the ‘training by research projects’ for ERs and ESRs employed by the LASSIE ITN that will be developed under our implementation plan. Figure 3 illustrates the depth and breadth of the interconnections between these themes and the LASSIE ITN partners.

WP1 - Formation of Grains, Small Molecules and Ices Top of page

Observations have shown that vast clouds of molecules and dust exist between the stars and the gravitational collapse of these clouds is the first step in the formation of new stars. Observational evidence further shows that in these clouds the dust grains are coated with icy mantles of small molecules, such as H2O, CO, CO2, NH3 and CH3OH. How do we account for the presence of the dust? What is it made of and what does it look like? How can we be sure of the veracity of observations that indicate the presence of these small molecules and their ices? These are questions that cannot be addressed by observation and modelling alone and laboratory measurement is crucial to help us identify what is out there and to understand its origin. It has become apparent in recent years that the neglect of heterogeneous chemistry in these clouds is a major shortcoming in the traditional “gas-only” models of interstellar chemistry. Hence we must address these questions from the standpoint of investigating heterogeneous processes at the gas-solid interface using realistic models of the relevant interfaces. Fortunately, we are now in a position where such heterogeneous processes can be studied in the laboratory in great detail, using a range of highly sophisticated techniques. These experiments can probe phenomena as varied as the structure of condensing carbon or silicate grains; the disposal of energy into the translation, rotation and vibration of newly formed molecules; and the rates of reactive accretion of icy layers and the morphology of those growing ice layers.

Aims and Objectives: Theme 1 will focus on the formation and optical properties of dust grains, 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. The theme will focus on experiments aimed at providing a basic understanding of grains and ices. For each task the primary contractor responsible for delivery is clearly identified by underlining. The primary contractor will be responsible for coordinating with the secondary contractors where multiple contractors are contributing to the effort.

WP2 - Physical Processes in and on Icy Grains Top of page

The dominant ice in the Universe is water ice. However observations tell us that icy grain mantles contain more than just water ice e.g. CO, CO2, and CH3OH. Furthermore, it is likely that these ices will be doped with small amounts of polycyclic aromatic and heteroaromatic hydrocarbons (PAHs) that are believed to be prevalent as a sink for carbon in the Universe. Moreover, some of these icy mixtures may exist in the form of crystalline solids such as clathrates. Understanding the physical processes that can occur in such an icy material is central to the LASSIE ITN. In particular, we are interested in the destruction of grains and their icy mantles as a mechanism for returning material to the gas phase. Physical destruction processes, driven in part by electromagnetic and particle irradiation, consist of thermal or photon/particle-induced desorption and evaporation, differentiation by selective evaporation, and sputtering. Grain-grain collisions may also play an important role, leading to both disruption of icy mantles and fragmentation of a grain cluster itself, and represent an important physical process undergone by grains (see theme 1). The groups involved in this research theme have excellent track records regarding the application of surface science in astronomy. Indeed, they have championed the application of ultrahigh vacuum methods within the community. Their contributions in studies of the thermally driven desorption from model icy grain mantles have had a major impact in astrochemistry in highlighting the role of ice morphology in modifying the thermal behaviour of ices, resulting in a paradigm shift within the community. In addition, their detailed studies of the infrared spectroscopy of CO and CO2 in and on water ices have been able to address long standing problems in comparing laboratory spectral data with observations.

Aims and Objectives: Our primary aim is to contribute to the understanding of the physical processes occurring when an icy mantle is subjected to electromagnetic radiation or bombarded with charged and/or neutral particles. For each task the primary contractor responsible for delivery is clearly identified by underlining. The primary contractor will be responsible for coordinating with the secondary contractors where multiple contractors are contributing to the effort.

WP3 - Chemical Transformations in and on Icy Grains Top of page

More than 150 different molecules have been identified in star-forming regions. These range from simple diatomic species such as CO to exotic radicals (e.g. linear HC5) and complex organic molecules like CH3OCH3 and CH3CH2CN. This chemical complexity has been explained for many years by gasphase processes driven by cosmic-ray ionization, but new models show that such processes only reproduce observed abundances of the smaller, open shell, species. New evidence shows that icy dust grains with temperatures as low as 10 K can act as catalytic sites for molecule formation and that the formation of the more complex species involves surface processes in ices adsorbed on interstellar grains. Two routes to complex organics have been proposed. First generation species are produced on surfaces through elementary exothermic hydrogen additions and reactions possessing activation-energy barriers of closed-shell species with H-, N-, O- or C-atoms. The reactivity is further enhanced by simultaneous energetic processing, due to UV irradiation and cosmic ray exposure. Later in the star formation sequence, during the ‘hot core’ phase, grains warm up to temperatures between 20 and 100 K and molecules desorb from the ices, bringing into the gas phase a new class of molecules that acts as a starting point for second generation species.

Aims and Objectives: The topic of research theme 3 is to study this evolution and to simulate the formation of complex molecules of astrophysical interest on grains and in interstellar ices under laboratory controlled conditions at an unprecedented level of detail and sensitivity. The majority of the participating groups in this theme have experience in growing interstellar ices on dust grain equivalents under high or ultrahigh vacuum (UHV) conditions dependent on ice morphology (chemical composition, amorphous versus crystalline structure, in pure, layered or mixed configurations), ice temperature and ice thickness. Within this theme the influence of different chemical trigger mechanisms will be quantified under conditions typical for inter- and circumstellar matter. The work plans for this theme is as below. For each task the primary contractor responsible for delivery is clearly identified by underlining. The primary contractor will be responsible for coordinating with the secondary contractors where multiple contractors are contributing to the effort.

WP4 - Modelling the Gas-Grain Interaction Top of page

Computational modelling of the gas-grain interaction provides further insights into the physics and chemistry underlying the relevant processes and relates macroscopic processes to interactions between individual atoms and molecules. Generally, the rates of surface reactions do not show a simple Arrhenius-like behaviour, since they are determined by a collection of different events such as deposition, diffusion, desorption, and chemical reaction parameters that cannot be easily controlled in the laboratory, but may be isolated and probed in computational models. Understanding these separate processes is of critical importance as we attempt to translate the total reaction rate to interstellar conditions, where fluxes are much lower than used in laboratory experiments. In this theme we will adopt quantum, Monte Carlo and classical modelling of icy systems to obtain information about the structure, spectroscopy and dynamics and allow the data obtained on laboratory timescales to be corrected for interstellar conditions. This theme therefore fulfils a key role in the scientific programme as it couples the experimental work of themes 1, 2 and 3 to the observation and modelling programme of theme 5.

Aims and Objectives: Our computational modelling programme is based around the work plan and identifiable tasks given in the table below. For each task the primary contractor responsible for delivery is clearly identified by underlining. The primary contractor will be responsible for coordinating with the secondary contractors where multiple contractors are contributing to the effort.

WP5 - Observations and Astronomical Models Involving Dust and Ices Top of page

The laboratory experiments and theoretical calculations described in themes 1 through 4 are the key to understanding the chemistry in interstellar clouds in which new stars and planets are formed. A particular strength of this network is the close interaction of chemists, physicists and astronomers, both within the various institutes and across nodes. Astronomical observations and modelling define the needs for laboratory experiments. In turn, the basic chemical data allow a much deeper understanding of the astrophysical data than otherwise possible.

In the vicinity of forming stars, in so called ‘hot cores’ (T > 100 K), many of the complex molecules observed in the gas phase are likely due to ices which have evaporated from the grains. The cores are warmed by the radiation as the star turns on, so that ices deposited on dust during the star-formation process are released to the gas phase and their emissions detected. Therefore, hot cores represent the integrated history of the physical conditions during the formation of the star. However, a key question is how these complex molecules form, whether by successive hydrogenation and oxidation of accreted gas-phase species, especially CO, or by processing of the ice by UV photons and charged particles, or by gas-phase reactions between evaporated species at high temperatures. A combination of these three processes is most likely the answer. The laboratory experiments described in themes 1 through 3 are essential to distinguish between these scenarios.

Following the star formation process, many young stars exhibit emission bands believed to originate from carbonaceous particles. These bands are often observed strongly in emission from the photondominated regions (PDRs) that surround massive star formation regions. The origin of these bands is, as yet, unresolved. We will make detailed observations of the strengths and relative intensities of these bands as a function of astrophysical environment, in order to correlate them with our laboratory investigations of surface chemical reactions on carbon surfaces.

Aims and Objectives: The primary goal of this theme is to obtain quantitative astronomical constraints on the role of grains in interstellar chemistry. This will be achieved through a combination of observations and modelling. The observational and molecular astrophysics groups within our network have a number of goals that closely link into the programme of laboratory science. These are summarised below. For each task the primary contractor responsible for delivery is clearly identified by underlining. The primary contractor will be responsible for coordinating with the secondary contractors where multiple contractors are contributing to the effort.