Letters of Intent for 2015

LoI 2015-188
Focus Meeting: Complex Organic Molecules in Space

Date: 3 August 2015 to 14 August 2015
Location: Honolulu, United States
Contact: Tom Millar (Tom.Millar@qub.ac.uk)
Coordinating division: Division H Interstellar Matter and Local Universe
Co-Chairs of SOC: T J Millar (Queen's University Belfast)
S Yamamoto (University of Tokyo)
Chair of LOC: N/A ()



• Observations of COMs in star-forming regions
• Observations of COMs in the Solar System
• Spectroscopy of COMs and their isotopologues
• Collisional and radiative excitation of COMs
• Gas-phase astrochemistry of COMs – theory and experiment
• Solid-state astrochemistry of COMs – theory and experiment
• COMs as probes of star-formation process
• The interstellar-Solar System connection
• COMS and the origin of life



The topic of complex organic molecules, hereafter COMs, has become a topic of intense debate in the astrochemical community in recent years. It is a debate that reflects the broad interests of astronomers from fields such as star formation, cometary science and astrobiology as well as the wider population of scientists from other disciplines, for example, those involved in gas-phase and solid-state spectroscopy and kinetics, surface scientists, and chemical physicists, who are keen to bring their expertise to bear on issues of astrophysical importance.

COMs, which we define for the purposes of the proposed focus meeting, are molecules containing five or more atoms, were first observed through the detection of carbon-chain molecules, such as the cyanopolyynes, HC2n+1N, and methyl-bearing species such as methanol, CH3OH and acetonitrile, CH3CN, in cold, dark clouds. The widespread use of these molecules to probe density, temperature and chemical evolution (history) of interstellar clouds led to a recognition of the importance of ion-neutral and neutral-neutral reactions in their formation, as well as to sensitive spectroscopic studies that have culminated in the recent detection of carbon-chain anions, C6H- and C8H- among others, in dark clouds and circumstellar envelopes.

In addition to these highly-unsaturated molecules, a second important class of COMs are the large, hydrogenated species such as ethanol, CH3CH2OH and dimethyl ether, CH3OCH3, that are observed towards hot molecular cores (HMCs), small, hot, dense clumps of gas in regions of massive star formation. Nowadays, they are known to exist in the vicinity of solar-type protostars called hot corinos. These species are observed to have very large abundances in such regions – saturated molecules are generally enhanced in abundance by a factor 103 – 105 over their cold cloud abundances – which, together with enhanced levels of deuterium fractionation, have been interpreted as a sign of an active, relatively low-temperature (20-50K), ice chemistry which becomes ‘observable’ when ice mantles are evaporated by nearby star formation. COMs provide rich line-emission in the sub-millimetre region and are routinely used to probe the physics and chemistry of high-mass star formation. Indeed, isotopologues and vibrational satellites of COMs are likely to provide the bulk of the many unidentified lines seen in HMC spectra, an issue which limits the interpretation of spectra and the underlying physics.

The importance of COMs as diagnostic probes has resulted in the creation of many laboratory astrophysics groups around the world that study, among other things, ice chemistry, surface binding energies and diffusion, and thermal and non-thermal evaporation processes. The traditional picture of COMs – unsaturated species made by gas-phase reaction in cold clouds and saturated species made by ice surface chemistry in warmer clouds – is under review due to the detection of species such as HC5N in HMCs and methyl formate and glycolaldehyde in cold clouds. We expect that, by the time of the GA, ALMA will have added significantly to our knowledge of the location, abundance, morphologies and correlations in COM species and will pose substantial further challenges – and perhaps some solutions – to our understanding of the relationship between COMs and star formation.

COMs have also been detected in comets, often with similar abundances to those observed in interstellar clouds and can provide insight into whether cometary ices preserve an interstellar, or predominantly interstellar, heritage. Organic materials which are considered to be of pre-solar origin are also found in carbonaceous meteorites and COMs have some of the basic complexity needed to aid in the formation of biological molecules in nascent stellar and planetary systems.

In this focus meeting, we shall bring together astronomers interested in star formation, cometary chemistry, and astrobiology with theoretical and experimental chemists and physicists to answer the following questions:

1. Can interstellar COMs be used to probe ice chemistry prior to star formation? Once evaporated, can they be used to infer the time-scale since star formation was initiated?
2. What are the key parameters that control ice chemistry at temperatures of 10-100K? What can laboratory experiments and theory tell us about binding energies, diffusion and desorption processes in ices?
3. Can we understand these processes sufficiently to interpret the high spatial resolution observations now available with ALMA to probe snow lines in the protoplanetary disks around stars of different?
4. Can we understand quantitatively the processes by which molecules are fractionated in deuterium in ices?
5. Is there evidence from COMs that cometary ices reflect an interstellar origin? What types of evidence would provide such evidence?
6. Can we relate observation of COMs in low-mass disk systems to processes in our own Solar System? Is there any relationship between COMs and pre-solar organic materials in meteorites?

This request for a 2-day long focus meeting is very timely, because ALMA will unveil the chemical compositions of protostellar and protoplanetary disks with unprecedented spatial resolution. This, along with many other advances in observations, laboratory experiments, and theoretical studies will enable stimulating and intensive discussions on COMs during this proposed meeting.