An Experimental Investigation of the Synthesis of Complex Organic Molecules in Interstellar Analog Ices


The overarching goal of this project is to explore experimentally in an innovative ultra-high vacuum space simulation chamber the formation of six key classes of complex organic molecules (COMs) – organic molecules containing atoms of carbon, hydrogen, oxygen, and nitrogen - upon interaction of ionizing radiation in the form of Lyman α photons with interstellar ice analog samples and to constrain the level of molecular complexity that can ultimately be synthesized in the interstellar medium (ISM). These key classes are aldehydes (HCOR), ketones (RCOR’), carboxylic acids (RCOOH), esters (RCOOR’), amides (RCONH2), and isocyanates (RNCO). Those objectives are achieved by systematically replicating the conditions of ice-coated interstellar grains in a next-generation ultra-high vacuum surface scattering machine through the exposure of interstellar ice analog samples resembling ices in cold molecular clouds as well as in low- and high-mass star forming regions at astrophysically relevant temperatures (10 K to 50 K) to ionizing radiation in form of Lyman α photons (10.2 eV). Compared to previous studies, we follow a radically different approach and apply a transformative methodology by probing the synthesis of COMs on line and in situ via complementary detection schemes in the condensed phase (Infrared, Raman, UVVIS) and upon sublimation of COMs into the gas phase via the progressive technology of tunable, fragment-free vacuum ultraviolet (VUV) photoionization. This unique space simulation chamber allows the extraction of transformative concepts on the synthesis of COMs in interstellar ices upon exposure to ionizing radiation by exploiting a novel technology through the implementation of cutting edge photoionization techniques.

Key classes of COMs detected in the ISM suggested to be formed on ice-coated interstellar grains. Molecules in bold were also detected in comet 67P/Churyumov–Gerasimenko.
Critical effect of non-equilibrium chemical reactions on the formation of complex organic molecules within interstellar ices. Solely gas phase reactions cannot reproduce the observed fractional abundances. The astrochemical models were carried out by the group of Prof. Eric Herbst (University of Virginia).

The unraveling of the formation of key classes of COMs is of core significance to the laboratory astrophysics and astronomy communities. First, our project advances the knowledge of the most fundamental processes leading to COMs on ice-coated interstellar grains in cold molecular clouds and in star forming regions. Since the transition from a molecular cloud to star forming regions depends on the molecular composition, it is imperative to unravel the processes of how COMs are formed in those environments; this also assists testing chemical models of molecular clouds and of star forming regions as these molecules may play a key role in astrobiology and their synthetic pathways are constrained by physical (temperature, radiation) and chemical (ice composition) conditions. Second, structural isomers – molecules with the same molecular formula but different connectivities of atoms – serve as a molecular ‘clock’ and ‘tracers’ in defining the evolutionary stage of cold molecular clouds and star forming regions. Here, the lack of data on products and rates of their formation and how they depend on the ice temperature and composition limits the understanding of how COMs are synthesized. In combination with astrochemical modeling, our project extracts transformative concepts on the formation of COMs on interstellar grains and defines an inventory of COMs constraining the level of molecular complexity that can ultimately be synthesized in space. Also, if a new COM is detected in the ISM, the agile management of our project allows a rapid implementation of fresh laboratory experiments and astrochemical modeling to unravel not only the underlying formation routes of this COM, but also its role in the astrochemical evolution of molecular clouds and star forming regions. Third, since COMs have also been identified in the Murchison meteorite and in comet 67P/Churyumov-Gerasimenko, our project might bring us closer to understanding the extent to which these key classes of COMs might have been synthesized exogenously in the ISM, (partly) incorporated into comets and parent bodies of, e.g., Murchison, and then delivered to early Earth.

Left: Benefits of fragment free single photon ionization. a): electron impact ionization (70 eV) fragmentation pattern of methyl formate (HCOOCH3). Note extensive fragmentation of the parent peak at m/z = 60 following electron impact; b) single photon fragment free ionization (10.9 eV) resulting in an intense molecular ion. Right: Sublimation profile of the molecular ion C3H6O+ (m/z = 58) after photoionization of the subliming molecules with 10.49 eV (a) and 9.92 eV (b) in irradiated carbon dioxide – propylene ices; the fits of the 9.92 eV experiment were subtracted from the 10.49 eV experiment (c); the result corresponds to signal from propylene oxide (c-C3H6O) (c). At a photon energy of 10.49 eV, all C3H6O isomers are ionized; at 9.92 eV, C3H6O isomers except propylene oxide are ionized.
Top view of the main chamber including the cryogenic target (point of converging lines), analytical instruments, and photolysis source. The source is aligned with respect to the target to allow for the simultaneous in situ monitoring of IR, Ra, and UV-VIS spectroscopies. The inset shows the geometry of the ReTOF lenses with respect to the target and ionization laser.
Overview of W.M. Keck Research Laboratory in Astrochemistry

Recent Selected Publications

1.   R.I. Kaiser, S. Maity, B.M. Jones, Synthesis of Prebiotic Glycerol in Interstellar Ices, Angew. Chem. Int. Ed., 54, 195-200 (2015).   (PDF)

2.   S. Maity, R.I. Kaiser, and B.M. Jones, Formation of complex organic molecules in methanol and methanol-carbon monoxide ice exposed to ionizing radiation - a combined FTIR and reflectron time-of-flight mass spectrometry study, Phys. Chem. Chem. Phys., 17, 3081 - 3114  (2015).   (PDF)

3.   M.J. Abplanalp, A. Borsuk, B.M. Jones, R.I. Kaiser, On the Formation and Isomer Specific Detection of Propenal (C2H3CHO) and Cyclpropanone (c-C3H4O) in Interstellar Model Ices-A Combined FTIR and Reflectron Time-of-Flight Mass Spectroscopic Study, Ap. J., 814, 45  (2015).   (PDF)

4.   M.J. Abplanalp, M. Förstel, and R.I. Kaiser, Exploiting single photon vacuum ultraviolet photoionization to unravel the synthesis of complex organic molecules in interstellar ices, Chemical Physics Letters, 644, 79-98  (2016).   (PDF)

5.   M. Förstel, P. Maksyutenko, B.M. Jones, B-J Sun, A.H.H. Chang, R. I. Kaiser, Synthesis of urea in cometary model ices and implications for Comet 67P/Churyumov-Gerasimenko, Chem. Comm. 52, 741-744  (2016).   (PDF)

6.   M. Förstel, P. Maksyutenko, A.M. Mebel, R.I. Kaiser, Pentacarbon dioxide (C5O2) formation and its role as a tracer of solar system evolution, Ap. J. L. 818:L30, 1-6  (2016).   (PDF)

7.   M. Förstel, P. Maksyutenko, B.M. Jones, B-J Sun, H.C. Lee, A.H.H. Chang, R.I. Kaiser, On the Formation of Amide Polymers via Carbonyl-Amino Group Linkages in Energetically Processed Ices of Apical Relevance, Ap. J. 820, 117  (2016).   (PDF)

8.   B.M. McMurtry, A.M. Turner, S.E.J. Saito, R.I. Kaiser, On the formation of Niacin (Vitamin B3) and Pyridine Carboxylic Acids in Interstellar Model Ices, Chemical Physics 472, 173  (2016).   (PDF)

9.   M.J. Abplanalp, S. Gozem, A.I. Krylov, C.N. Shingledecker, E. Herbst, R.I. Kaiser, A study of interstellar aldehydes and enols as tracers of a cosmic ray-driven nonequilibrium synthesis of complex organic molecules, Proceedings of the National Acadamy of Sciences 113, 7727-7732  (2016).   (PDF)

10.   M.J. Abplanalp, R. I. Kaiser, Complex hydrocarbon chemistry in interstellar and solar system ices revealed: a combined infrared spectroscopy and reflectron time-of-flight mass spectrometry analysis of ethane (C2H6) and D6-ethane (C2D6) ices exposed to ionizing radiation, Ap. J., 827, 132  (2016).   (PDF)

11.   B.M. McMurtry, S.E.J. Saito, A.M. Turner, H.K. Chakravarty, R.I. Kaiser, On the Formation of Benzoic Acid and Higher-Order Benzene Carboxylic Acids in Interstellar Model Ice Grains, Ap. J., 831, 174  (2016).   (PDF)

12.   A. Bergantini, R.I. Kaiser. In Situ Detection of Organics in the Comet 67P/Churyumov-Gerasimenko, Chem 1(6), 822-829  (2016).   (PDF)

13.   M.J. Abplanalp, R.I. Kaiser, Implications for Extraterrestrial Hydrocarbon Chemistry: Analysis of Ethylene (C2H4) and D4-Ethylene (C2D4) Ices Exposed to Ionizing Radiation via Combined Infrared Spectroscopy and Reflectron Time-of-flight Mass Spectrometry, J. ApJ, 836, 195  (2017).   (PDF)

14.   A. Bergantini, Pavlo Maksyutenko, R.I. Kaiser, On the Formation of the C2H6O Isomers Ethanol (C2H5OH) and Dimethyl Ether (CH3OCH3) in Star-forming Regions, Ap. J., 841:96, 1-24  (2017).   (PDF)

15.   M. Förstel, A. Bergantini, P. Maksyutenko, S. Góbi, R.I. Kaiser, Formation of Methylamine and Ethylamine in Extraterrestrial Ices and Their Role as Fundamental Building Blocks of Proteinogenic α-amino Acids, Ap. J., 845, 83  (2017).   (PDF)

16.   M.J. Abplanalp, B.M. Jones, R.I. Kaiser, Untangling the methane chemistry in interstellar and solar system ices toward ionizing radiation: a combined infrared and reflectron time-of-flight analysis, Phys. Chem. Chem. Phys., 20, 5435-5468  (2018).   (PDF)

17.   Y.A. Tsegaw, S. Góbi, M. Förstel, P. Maksyutenko, W. Sander, R.I. Kaiser, Formation of Hydroxylamine in Low-Temperature Interstellar Model Ices, J. Phys. Chem. A, 121, 7477-7493  (2017).   (PDF)

18.   A. Bergantini, S. Góbi, M.J. Abplanalp, R.I. Kaiser, A Mechanistical Study on the Formation of Dimethyl Ether (CH3OCH3) and Ethanol (CH3CH2OH) in Methanol-containing Ices and Implications for the Chemistry of Star-forming Regions, ApJ, 852, 70  (2018).   (PDF)

19.   C. Zhu, A.M. Turner, M.J. Abplanalp, R.I. Kaiser, Formation of High-order Carboxylic Acids (RCOOH) in Interstellar Analogous Ices of Carbon Dioxide (CO2) and Methane(CH4), ApJS, 234, 15  (2018).   (PDF)

20.   M.J. Abplanalp, S. Góbi, A.Bergantini, A.M. Turner, R.I. Kaiser, On the Synthesis of Chocolate Flavonoids (Propanols, Butanals) in the Interstellar Medium, Chem. Phys. Chem. 19, 556-560  (2018).   (PDF)

21.   A. Bergantini, R. Frigge, R.I. Kaiser Constraining the Molecular Complexity in the Interstellar Medium-The Formation of Ethyl Methyl Ether (CH3OCH2CH3) in Star-forming Regions, The Astrophysical Journal 859, 59  (2018).   (PDF)

22.   A. Bergantini, M.J. Abplanalp, P. Pokhilko, A.I. Krylov, C.N. Shingledecker, E. Herbst, R.I. Kaiser, A Combined Experimental and Theoretical Study on the Formation of Interstellar Propylene Oxide (CH3CHCH2O)-A Chiral Molecule, The Astrophysical Journal 860, 108  (2018).   (PDF)

23.   R. Frigge, C. Zhu, A.M. Turner, M.J. Abplanalp, A. Bergantini, B-J Sun, Y-L Chen, A.H.H. Chang, R. I. Kaiser, A Vacuum Ultraviolet Photoionization Study on the Formation of N-methyl Formamide (HCONHCH3) in Deep Space: A Potential Interstellar Molecule with a Peptide Bond, The Astrophysical Journal 862, 84  (2018).   (PDF)

24.   A. Bergantini, C. Zhu, R.I. Kaiser, A Photoionization Reflectron Time-of-flight Mass Spectrometric Study on the Formation of Acetic Acid (CH3COOH) in Interstellar Analog Ices, The Astrophysical Journal 862, 140  (2018).   (PDF)

25.   C. Zhu, R. Frigge, A.M. Turner, M.J. Abplanalp, B.-J. Sun, Y.-L. Chen, A.H.H. Chang, R. I. Kaiser, A vacuum ultraviolet photoionization study on the formation of methanimine (CH2NH) and ethylenediamine (NH2CH2CH2NH2) in low temperature interstellar model ices exposed to ionizing radiation, Phys. Chem. Chem. Phys. 21, 1952-1962, (2019).   (PDF)