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Title: Hydrogenation and Deuteration of C{sub 2}H{sub 2} and C{sub 2}H{sub 4} on Cold Grains: A Clue to the Formation Mechanism of C{sub 2}H{sub 6} with Astronomical Interest

Abstract

We quantitatively investigated the hydrogen addition reactions of acetylene (C{sub 2}H{sub 2}) and ethylene (C{sub 2}H{sub 4}) on amorphous solid water (ASW) at 10 and 20 K relevant to the formation of ethane (C{sub 2}H{sub 6}) on interstellar icy grains. We found that the ASW surface enhances the reaction rates for C{sub 2}H{sub 2} and C{sub 2}H{sub 4} by approximately a factor of 2 compared to those on the pure-solid C{sub 2}H{sub 2} and C{sub 2}H{sub 4} at 10 K, probably due to an increase in the sticking coefficient and adsorption energy of the H atoms on ASW. In contrast to the previous proposal that the hydrogenation rate of C{sub 2}H{sub 4} is orders of magnitude larger than that of C{sub 2}H{sub 2}, the present results show that the difference in hydrogenation rates of C{sub 2}H{sub 2} and C{sub 2}H{sub 4} is only within a factor of 3 on both the surfaces of pure solids and ASW. In addition, we found the small kinetic isotope effect for hydrogenation/deuteration of C{sub 2}H{sub 2} and C{sub 2}H{sub 4} at 10 K, despite the requirement of quantum tunneling. At 20 K, the reaction rate of deuteration becomes even larger than that of hydrogenation.more » These unusual isotope effects might originate from a slightly larger number density of D atoms than H atoms on ASW at 20 K. The hydrogenation of C{sub 2}H{sub 2} is four times faster than CO hydrogenation and can produce C{sub 2}H{sub 6} efficiently through C{sub 2}H{sub 4} even in the environment of a dark molecular cloud.« less

Authors:
;  [1]; ; ;  [2]; ;  [3]
  1. Koyama Astronomical Observatory, Kyoto Sangyo University Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555 (Japan)
  2. Institute of Low Temperature Science, Hokkaido University N19-W8, Kita-ku, Sapporo, Hokkaido 060-0819 (Japan)
  3. Institute for Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart (Germany)
Publication Date:
OSTI Identifier:
22661282
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 837; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ADSORPTION; AMORPHOUS STATE; CARBON MONOXIDE; DEUTERATION; HYDROCARBONS; HYDROGENATION; ICE; MOLECULES; SIMULATION; SPACE; TEMPERATURE RANGE 0013-0065 K; TUNNEL EFFECT

Citation Formats

Kobayashi, Hitomi, Kawakita, Hideyo, Hidaka, Hiroshi, Hama, Tetsuya, Watanabe, Naoki, Lamberts, Thanja, and Kästner, Johannes, E-mail: h_kobayashi@kyoto-nijikoubou.com. Hydrogenation and Deuteration of C{sub 2}H{sub 2} and C{sub 2}H{sub 4} on Cold Grains: A Clue to the Formation Mechanism of C{sub 2}H{sub 6} with Astronomical Interest. United States: N. p., 2017. Web. doi:10.3847/1538-4357/837/2/155.
Kobayashi, Hitomi, Kawakita, Hideyo, Hidaka, Hiroshi, Hama, Tetsuya, Watanabe, Naoki, Lamberts, Thanja, & Kästner, Johannes, E-mail: h_kobayashi@kyoto-nijikoubou.com. Hydrogenation and Deuteration of C{sub 2}H{sub 2} and C{sub 2}H{sub 4} on Cold Grains: A Clue to the Formation Mechanism of C{sub 2}H{sub 6} with Astronomical Interest. United States. doi:10.3847/1538-4357/837/2/155.
Kobayashi, Hitomi, Kawakita, Hideyo, Hidaka, Hiroshi, Hama, Tetsuya, Watanabe, Naoki, Lamberts, Thanja, and Kästner, Johannes, E-mail: h_kobayashi@kyoto-nijikoubou.com. Fri . "Hydrogenation and Deuteration of C{sub 2}H{sub 2} and C{sub 2}H{sub 4} on Cold Grains: A Clue to the Formation Mechanism of C{sub 2}H{sub 6} with Astronomical Interest". United States. doi:10.3847/1538-4357/837/2/155.
@article{osti_22661282,
title = {Hydrogenation and Deuteration of C{sub 2}H{sub 2} and C{sub 2}H{sub 4} on Cold Grains: A Clue to the Formation Mechanism of C{sub 2}H{sub 6} with Astronomical Interest},
author = {Kobayashi, Hitomi and Kawakita, Hideyo and Hidaka, Hiroshi and Hama, Tetsuya and Watanabe, Naoki and Lamberts, Thanja and Kästner, Johannes, E-mail: h_kobayashi@kyoto-nijikoubou.com},
abstractNote = {We quantitatively investigated the hydrogen addition reactions of acetylene (C{sub 2}H{sub 2}) and ethylene (C{sub 2}H{sub 4}) on amorphous solid water (ASW) at 10 and 20 K relevant to the formation of ethane (C{sub 2}H{sub 6}) on interstellar icy grains. We found that the ASW surface enhances the reaction rates for C{sub 2}H{sub 2} and C{sub 2}H{sub 4} by approximately a factor of 2 compared to those on the pure-solid C{sub 2}H{sub 2} and C{sub 2}H{sub 4} at 10 K, probably due to an increase in the sticking coefficient and adsorption energy of the H atoms on ASW. In contrast to the previous proposal that the hydrogenation rate of C{sub 2}H{sub 4} is orders of magnitude larger than that of C{sub 2}H{sub 2}, the present results show that the difference in hydrogenation rates of C{sub 2}H{sub 2} and C{sub 2}H{sub 4} is only within a factor of 3 on both the surfaces of pure solids and ASW. In addition, we found the small kinetic isotope effect for hydrogenation/deuteration of C{sub 2}H{sub 2} and C{sub 2}H{sub 4} at 10 K, despite the requirement of quantum tunneling. At 20 K, the reaction rate of deuteration becomes even larger than that of hydrogenation. These unusual isotope effects might originate from a slightly larger number density of D atoms than H atoms on ASW at 20 K. The hydrogenation of C{sub 2}H{sub 2} is four times faster than CO hydrogenation and can produce C{sub 2}H{sub 6} efficiently through C{sub 2}H{sub 4} even in the environment of a dark molecular cloud.},
doi = {10.3847/1538-4357/837/2/155},
journal = {Astrophysical Journal},
number = 2,
volume = 837,
place = {United States},
year = {Fri Mar 10 00:00:00 EST 2017},
month = {Fri Mar 10 00:00:00 EST 2017}
}