Astrochemistry Discussions are tentatively scheduled every other week beginning 22 April, 2020. The plan is for the Main Event to run 14:00 - 15:00 UTC. Some weeks may be followed by casual conversations, a meet and greet, etc. from 15:00 - 15:30 UTC.
A Google Calendar is provided here that you can add to your own, and should display in your local timezone (baring VPN issues - see the note at the bottom of the calendar to see what time zone it thinks you're in).
Things will certainly evolve with time as we figure out the system that works best for everyone.
From Hot-corinos to our chemical heritage; the case of NGC1333 IRAS 4A
Studying the physical and chemical properties of low mass star systems is very important as it is directly related to the Solar-like system. Hot-corinos are low mass young stellar objects (YSOs) where the temperature is high enough (>100 K) to release ice-phase complex organic molecules into the gas environment and these COMs can be detected using observation in millimeter wavelength. Some of the COMs are prebiotic and may be related to our chemical heritage. In this talk, I will focus on a protobinary system NGC1333 IRAS 4A and will discuss the presence of hot-corino and an upper limit calculation of a glycine isomer, methyl carbamate. Glycine is a prebiotic molecule, in this connection, I will also discuss how possibly our chemical heritage can be maintained from the early stage of a low mass star formation to planetary objects like our Sun-Earth system.
Molecular spectroscopic line lists
The rapid rise in interest in exoplanetary atmospheres has led to an explosion of interest by astronomers in high accuracy and comprehensive small molecule spectroscopy data. This data is needed to understand and characterise these exoplanetary atmospheres and their host stars (including soon the scientific search for the molecules of life). In this talk, I will discuss in depth a key type of data desired by astronomers - the molecular spectroscopic line list - and how this data is produced by myself and others based on laboratory spectroscopy experiments and high level ab-initio electronic structure calculations, focusing on the key example of diatomic TiO.
The demands for accuracy and breadth of spectral coverage are substantial. New high-resolution techniques now mean that astronomers need these line lists to have strong lines frequencies to an accuracy of < 0.3 cm-1. Simultaneously, very weak lines must be considered to ensure accurate opacities can be calculated, leading to databases of millions to billions of spectral lines per molecule.
New solid-state environments for the formation of complex organics
Spacecraft exploration of icy outer Solar System bodies such as Titan has alluded to a rich cyanide chemistry. Here, the recombination of radicals, atoms, and ions - generated by photolysis and energetic particle interactions with methane and molecular nitrogen - generate a wide variety complex organic molecules. Such chemistry has been the inspiration for many laboratory investigations over the past decades where cyanides have been a particular focus as they present as carriers of C-N bonds required for species of biological interest such as N-bearing heterocycles.
This short talk will focus on structural and spectroscopic characterisation of cyanide-bearing molecular co-crystals. Perhaps most relevant to the aerosols of Titan’s atmosphere - where fractional condensation of nitriles and hydrocarbons are expected to yield ices of mixed composition - these particles could generate higher order organics via interactions with cosmic rays that penetrate through to the surface. In our preliminary studies on cyanide co-crystals, we have used periodic-DFT to predict the ternary-phase 2C6H6-C2H2-HCN crystal; a system that shows competitive thermochemistry under Titan conditions. These co-crystal compositions, where polar nitrile species are completely mixed with hydrocarbon material in stable molecular arrangements, provide new environments to explore efficient solid-state chemistry. We discuss our recent endeavours in this pursuit.
Ennis, C.; Cable, M.; Hodyss, R. & Maynard-Casely, H. “Mixed Hydrocarbon and Cyanide Ice Compositions for Titan’s Atmospheric Aerosols: A Ternary-Phase Co-crystal Predicted by Density Functional Theory” ACS Earth Space Chem (2020). DOI: 10.1021/acsearthspacechem.0c00130
Making a Habitable Planet
23 September, 2020 - 14:00 UTC
Department of Astronomy, University of Michigan
Today we stand on the cusp of characterizing potentially living worlds, or habitable planets, planets with orbits where liquid water would exist on a rocky surface. This concept of habitability implicitly assumes water in some form is present on rocky planets - but is it? More broadly are rocky planets generally "chemically habitable" - do they contain the elements needed for life, such as carbon and nitrogen, on their surfaces? In this talk, I will review what we know about the chemical habitability of forming planets. I will follow the most abundant volatile elements needed for life (C, H, O, N) from the vast cold and low pressure environs of the interstellar space to their presence on planetary surfaces of worlds such as our own. I will outline our current understanding of star and planetary birth while discussing the fate of primary carriers of life's elements, both volatile species (e.g. H2O, CO, CO2) and more refractory materials (e.g. silicates, aliphatic/aromatic hydrocarbons). Some of these carriers can be characterized via existing facilities (e.g. the Atacama Large Millimeter Array), planned facilities (the James Webb Space Telescope), while others require future options (such as the Origins Space Telescope). Finally, within a young planet, the ultimate fate of delivered material is not set until the hot young terrestrial world solidifies and core formation ceases - thus the process of planet formation and evolution itself influences whether a mature planet is habitable or uninhabitable. Looking forward, the astrochemical study of life's materials in space, and the astronomical characterization of terrestrial exoplanets, must be intimately linked to grounding knowledge from the planetary sciences. A fascinating interdisciplinary future awaits, where we will seek to ascertain the origin of our own biosphere and provide crucial chemical context for habitability.
Black in Astrochem Workshop and Networking
When: 15 July 2020; 14:00 UTC
Ashley Walker, Ayanna Jones, Bryne Hadnott, Kathleen Rink, and William Jackson
Theoretical Tools For Astrochem Tutorial/Workshop - 8 July, 2020
Using reaction rate theory (MESMER) to provide robust kinetic parameters for astrochemical modelling
Experiments provide kinetic parameters, rate coefficients and product yields, over a limited range of temperatures and pressures. Often this experimental temperature range is not sufficient to cover the temperatures required for astrochemical modelling. Traditionally, simple analytical forms are used to represent rate coefficients, e.g.
k = A Tn exp(-Ea/RT).
However, this approach can result in extrapolated rate coefficients with an order of magnitude uncertainty, especially at very low temperatures.
A more robust approach is to use a theoretical model to fit to the experimental data before extrapolation. For a given reaction, the reaction rate theory code MESMER calculates rate parameters from the information provided by ab initio structure calculations. In addition, MESMER allows the theoretical parameters to be adjusted to best fit the data, and thus provide a robust description of the reaction. The reaction between the hydroxyl radical, OH, and formaldehyde, H2CO, will be used to illustrate how MESMER can provide robust rate coefficients down to 5 K.
Simulation of Reactivity on the Surface of Dust Grains: Pitfalls and Opportunities
Gas-phase reaction rates can often be predicted with high accuracy because only a few atoms are involved. Compared to that, the simulation of reactions happening on the surface of a dust grain is much more involved, which often requires compromises concerning accuracy. They are very valuable, however, since the corresponding experiments also face the problem of many parameters that have to be controlled. I will give an overview of techniques to model adsorption and surface reactivity, their estimated accuracy, and their computational costs. It turns out that even an "active" surface, like ASW, often has rather little influence on the reaction barriers. Nevertheless, such surfaces influence the reactivity - but can be treated by a very efficient implicit surface model.
Astrochemical Snow Day! - 24 June, 2020
Interstellar Comets: A New Window into the Diversity of Protoplanetary Disk Midplane Chemistry
Comets contain a crucial record of the chemistry that occurred in the proto-Solar accretion disk during the epoch of formation of our planets. The recent discovery of interstellar comets provides a unique opportunity to measure the composition of planetary materials originating around other stars. Consequently, we are entering a new era of Galactic astronomy, with the ability to directly investigate the chemistry that occurred in the disk midplanes of extrasolar planetary systems. This talk will summarise our knowledge of the recently-detected interstellar objects 1I/'Oumumua and 2I/Borisov, focusing on our ALMA observations of gas-phase CO and HCN in 2I/Borisov. While the HCN abundance relative to water (~0.11%) was similar to that found in typical Solar System comets, the CO abundance (~68%) was among the highest observed in any comet within 2 au of the Sun, revealing a likely origin in a CO-enriched environment. The importance of this finding in the context our understanding of cometary and protoplanetary disk chemistry - in particular, the ice chemistry occurring close to the CO snowline - will be discussed.
Merel van't Hoff
Imaging the H2O and CO snowlines around young stars
Planets form in disks of gas and dust around young stars. With the discovery of more than 4000 exoplanets and the ability to study circumstellar disks in great detail we can begin to address the question of how the composition of a planet is linked to its birth environment. Key aspects of circumstellar-disk chemistry are snowlines: radii at which molecular species freeze out from the gas onto dust grains. The temperature at which a molecule freezes out is species dependent. The radial temperature profile in the disk therefore results in radial gradients in the chemical composition, for example, the elemental C/O-ratio of both the gas and ice. The bulk composition of planets may therefore be regulated by their formation location with respect to major snowlines. In this talk I will focus on how we can determine the locations of the two most important snowlines, the H2O and CO snowlines, observationally.
Infrared Resonant Vibrationally Induced Restructuring of Amorphous Solid Water
Amorphous solid water (ASW) is abundantly present in the interstellar medium, where it forms a mantle on interstellar dust particles and it is the precursor for cometary ices. In space, ASW acts as substrate for interstellar surface chemistry leading to complex molecules and it is postulated to play a critical role in proton-transfer reactions. Although ASW is widely studied and is generally well characterized by different techniques, energetically induced structural changes, such as ion, electron and photon irradiation, in these materials are less well understood. Selective pumping of specific infrared (IR) vibrational modes can aid in understanding the role of vibrations in restructuring of hydrogen bonding networks. In this talk, I will present the first experimental results on hydrogen bonding changes in ASW induced by the intense, nearly monochromatic mid-IR free-electron laser (FEL) radiation of the FELIX-2 beamline at the FELIX Laboratory at the Radboud University in Nijmegen, the Netherlands. Experiments are complimented with Molecular Dynamics simulations to constrain the effect at the molecular level.
Co-Authors: Jennifer A. Noble, Herma M. Cuppen, Stephane Coussan, Britta Redlich
Shocks! - Postponed
A themed special session on the astrochemistry and astrophysics of interstellar shocks.
Confirmed Invited Speakers
Women in Astrochemistry Meet & Greet - 20 May 2020
Ewine F. van Dishoeck
Ewine F. van Dishoeck is professor of molecular astrophysics at Leiden University, the Netherlands and external scientific member at MPE Garching. She graduated at Leiden in 1984 and held positions at Harvard, Princeton and Caltech before returning to Leiden in 1990. The work of her group innovatively combines the world of chemistry with that of physics and astronomy to study the molecular trail from star-forming clouds to planet-forming disks. She has mentored several dozens of students and postdocs and has been heavily involved in planning new observational facilities such as the Herschel Space Observatory, the Atacama Large Millimeter Array and the James Webb Space Telescope.
Ewine has been fortunate to receive many awards, including the 2000 Dutch Spinoza award, the 2015 Albert Einstein World Award of Science, and the 2018 Kavli Prize for Astrophysics. She is a Member or Foreign Associate of several academies, including that of the Netherlands, USA, Germany, Norway and Russia. Since 2007, she is the scientific director of the Netherlands Research School for Astronomy (NOVA). She was secretary and president of the IAU Working Group on Astrochemistry from 1991-2011, and co-responsible for four IAU Symposia in the field. As of 2018, Ewine serves as the president of the International Astronomical Union (IAU).
Leah Dodson is a brand new Assistant Professor in the Department of Chemistry & Biochemistry at the University of Maryland College Park. Her interests lie in using experimental physical chemistry techniques to investigate the chemical reactions that occur in the interstellar medium and in planetary atmospheres. Her group uses cryogenic and vacuum technology, spectroscopy, and mass spectrometry to study the kinetics and dynamics of astrochemical reactions under the low-temperature conditions relevant to these environments.
Leah received her B.S. in Chemistry in 2010 from Case Western Reserve University and her Ph.D. in Chemistry in 2016 from California Institute of Technology, working with Mitchio Okumura. Her thesis work focused on studying hydrocarbon oxidation and radical chemistry relevant to atmospheric and combustion chemistry and included collaborations with the Combustion Research Facility at Sandia National Labs and the Advanced Light Source at Lawrence Berkeley National Lab. She completed her postdoctoral work with Mathias Weber at NIST/JILA/University of Colorado Boulder before joining the UMD faculty in 2019.
Cosmic Rays Day! 6 May 2020
The Effects of Cosmic Rays on Carbon Chemistry
Cosmic rays (CRs) are energetic charged particles accelerated in extreme environments. Galactic CRs are accelerated primarily through supernovae. However, it has been recently proposed that protostars may be able to accelerate CRs. These cosmic rays will substantially alter the carbon chemistry in molecular gas. I will present astrochemical calculations of the impact of different CR populations and physics on carbon chemistry. The calculations were performed on a modified version of the publicly available astrochemistry code, 3D-PDR, in which CR attenation has been included in-situ. As such, we're to directly study the impact of different external and internal CR spectra. We find embedded sources of CRs significantly impact the carbon chemistry in relation to the HI-to-Hw transition. The dense gas is heated above 50 K and bright in [CII] emission. Embedded CR sources allow for atomic carbon to exist in dense gas where traditional models have carbon locked into carbon monoxide. Finally, I will show that the CO-to-H2 conversion factor used in extragalactic studies is relatively stable to significant enhancements of the CR ionization rate. However, the CI-to-H2 conversion factor is sensitive to the CR ionization rate and external environment.
Probing Galactic Cosmic Rays with Small Molecules
In the century following their discovery by Victor Hess in 1912, cosmic rays have been recognized as an important constituent of the Galaxy. With a total energy density somewhat larger than that of starlight, cosmic rays are the dominant source of ionization for the cold neutral medium (CNM) within the Galactic ISM. In starless molecular cloud cores, they are also the dominant source of heating. Thus, cosmic rays play a central role in astrochemistry by initiating a rich ion-neutral chemistry that operates within the CNM, and the cosmic-ray ionization rate (CRIR) is a key parameter in models for the chemistry of the ISM. In this talk, I will discuss recent estimates for the cosmic-ray ionization rate in the Galactic disk, obtained by using a detailed model for the physics and chemistry of diffuse interstellar gas clouds to interpret previously-published measurements of the abundance of four molecular ions: ArH+, OH+, H2O+ and H3+. The CRIR estimates thereby obtained show a remarkably small dispersion from one interstellar cloud to another. At the Galactocentric distance of the Sun, the primary CRIR per H nucleus is ~ 2x10-16 s-1 in both diffuse atomic clouds and diffuse molecular clouds. I will also discuss a recently-selected SOFIA Joint Legacy Program, HyGAL, which (among other things) will greatly expand the number of sight-lines on which ArH+, OH+, and H2O+ have been observed.
Cosmic Rays and Grain Chemistry in Star- and Planet-Forming Regions
Interstellar matter is subjected to bombardment by several types of ionizing radiation including cosmic rays, stellar winds, x-rays, and gamma-rays. It is known that such radiation can have a significant physicochemical impact on interstellar environments, and a large body of experimental work has shown that the interaction between such energetic particles and low-temperatures ices can result in the formation of complex - even prebiotic - molecules. Even so, modeling the chemical effects of cosmic ray collisions with interstellar dust grain ice mantles has proven challenging due to the complexity and variety of the underlying physical processes. In this talk, recent work on this subject by us is reviewed and the possible applications to better understanding the chemistry in star and planet-forming regions is highlighted.
From Clouds to Planets, The Astrochemical Link
22 April, 2020 - 14:00 UTC
All ingredients to make stars like our Sun and planets like our Earth are present in the dense (~100,000 H2 molecules per cc) and cold (~10 K) interstellar clouds. In these "stellar-system precursors" an active chemistry is already at work, as demonstrated by the presence of a rich variety of organic molecules in the gas phase and icy mantles encapsulating the sub-micrometer dust grains, the building blocks of planets. Here, I’ll present a journey from the earliest phases of star formation to protoplanetary disks, with links to our Solar System, highlighting the crucial role of astrochemistry as powerful diagnostic tool of the various steps present in the journey.