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Title: Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule

Abstract

Propylene oxide was recently identified in the interstellar medium, but few laboratory results are available for this molecule to guide current and future investigations. To address this situation, here we report infrared spectra, absorption coefficients, and band strengths of solid propylene oxide along with the first measurement of its refractive index and a calculation of its density, all for the amorphous solid form of the compound. We present the first experimental results showing a low-temperature formation pathway for propylene oxide near 10 K in interstellar ice analogs. Connections are drawn between our new results and the interstellar molecules propanal and acetone, and predictions are made about several as yet unobserved vinyl alcohols and methylketene. Comparisons are given to earlier laboratory work and a few applications to interstellar and solar system astrochemistry are described.

Authors:
;  [1];  [2]
  1. Astrochemistry Laboratory (Code 691), NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  2. Department of Chemistry, Kutztown University, Kutztown, PA 19530 (United States)
Publication Date:
OSTI Identifier:
22663900
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTRA; ACETONE; ALCOHOLS; COMPARATIVE EVALUATIONS; DENSITY; FORECASTING; ICE; INFRARED SPECTRA; INTERSTELLAR SPACE; MOLECULES; OXIDES; PROPYLENE; REFRACTIVE INDEX; SOLAR SYSTEM; SOLIDS

Citation Formats

Hudson, R. L., Loeffler, M. J., and Yocum, K. M., E-mail: Reggie.Hudson@nasa.gov. Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/225.
Hudson, R. L., Loeffler, M. J., & Yocum, K. M., E-mail: Reggie.Hudson@nasa.gov. Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule. United States. doi:10.3847/1538-4357/835/2/225.
Hudson, R. L., Loeffler, M. J., and Yocum, K. M., E-mail: Reggie.Hudson@nasa.gov. Wed . "Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule". United States. doi:10.3847/1538-4357/835/2/225.
@article{osti_22663900,
title = {Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule},
author = {Hudson, R. L. and Loeffler, M. J. and Yocum, K. M., E-mail: Reggie.Hudson@nasa.gov},
abstractNote = {Propylene oxide was recently identified in the interstellar medium, but few laboratory results are available for this molecule to guide current and future investigations. To address this situation, here we report infrared spectra, absorption coefficients, and band strengths of solid propylene oxide along with the first measurement of its refractive index and a calculation of its density, all for the amorphous solid form of the compound. We present the first experimental results showing a low-temperature formation pathway for propylene oxide near 10 K in interstellar ice analogs. Connections are drawn between our new results and the interstellar molecules propanal and acetone, and predictions are made about several as yet unobserved vinyl alcohols and methylketene. Comparisons are given to earlier laboratory work and a few applications to interstellar and solar system astrochemistry are described.},
doi = {10.3847/1538-4357/835/2/225},
journal = {Astrophysical Journal},
number = 2,
volume = 835,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}
  • Here, the adsorption of enantiopure versus racemic propylene oxide (PO) on Pd(111) is studied by temperature-programmed desorption (TPD) to explore possible differences in their saturation coverage. It is found that that the saturation coverage of enantiopure PO on Pd(111) is identical to that of racemic PO, in contrast to results on Pt(111) where significant coverage differences were found. The surface structures of enantiopure PO on Pd(111) were characterized by scanning tunneling microscopy (STM), which shows the formation of linear chains and hexagonal structures proposed to be due to freely rotating PO, in contrast to the relatively disordered PO overlayers foundmore » on Pt(111). STM experiments were carried out for enantiopure glycidol, which contains the same epoxy ring as PO, but where the methyl group of propylene oxide is replaced by a -CH 2OH group to provide a hydrogen-bonding sites. Glycidol STM images show the formation of completely different surface structures; at low coverages, glycidol forms pseudohexagonal structures which assemble from glycidol dimers, while at high coverages the surface shows extensive hydrogen-bonded networks. Density functional theory (DFT) calculations were carried out to model the enantiopure PO linear chain and the glycidol dimers that are observed by STM. Similar calculations were carried out for racemic PO and glycidol structures. The calculated interaction energies for the enantiopure and the racemic pairs reveal that there is no difference for homochiral versus heterochiral structures for both PO and glycidol on Pd(111).« less
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