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Journal of Chemical Physics / Volume 134 / Issue 6 / ARTICLES / Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

J. Chem. Phys. 134, 064315 (2011); http://dx.doi.org/10.1063/1.3532089 (10 pages)

Lyman-α driven molecule formation on SiO2 surfaces—connection to astrochemistry on dust grains in the interstellar medium

M. Rajappan, C. Yuan, and J. T. Yates, Jr.

Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, USA

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(Received 24 September 2010; accepted 7 December 2010; published online 11 February 2011)

As a model for silicate dust grains in the interstellar medium, we have used high area amorphous SiO2 as a surface on which to carry out Lyman-α (10.2 eV) photodecomposition of adsorbed N2O at 71 K and at a coverage of ∼0.3 monolayer. The N2O molecules are adsorbed by hydrogen bonding to surface Si-OH groups. Transmission IR spectroscopy measurements permit the observation of the consumption of adsorbed N2O and the production of various photoproducts. It is observed that in comparison to N2O consumption, the relative rate of formation of the products NO2 and N2O4 made by combination reactions is enhanced significantly on the SiO2 surface. Reactions between photogenerated radicals themselves or between radicals and parent N2O on the SiO2 surface exceed the relative rates observed in the gas phase by factors of up to ∼20. As the complexity of the combination product increases, its relative production rate, compared to the gas phase, increases due to the involvement of multiple surface-combination elementary steps. It is proposed that the enhancement of combination reactions on the SiO2 surface is due to the surface's ability to absorb excess energy evolved during the chemical-bond-forming events on the surface. This principle is probably significant on grain surfaces supporting photochemical processes of astrochemical interest, and indeed is expected. The cross section for adsorbed N2O photodecomposition on the porous SiO2 surface is about 7 × 10−20 cm2 and the quantum yield for the adsorbed molecule decomposition is about 0.006, compared to a quantum yield of 1.46 in the gas phase. This decrease in photon efficiency is attributed to absorption and scattering of Lyman-α radiation by the SiO2 particles.

© 2011 American Institute of Physics

Article Outline

  1. INTRODUCTION
  2. EXPERIMENTAL
    1. Lyman-α flux at SiO 2 sample
    2. SiO 2 sample preparation and mounting
    3. Control experiments—heating by Lyman-α lamp
    4. Gas phase N 2 O photochemistry
    5. N 2 O gas adsorption
    6. IR spectral measurements
    7. The availability of surface sites for photochemistry—comparison of gas phase to adsorbed phase measurements
  3. RESULTS
    1. Photostability of Si-OH groups by Lyman-α radiation
    2. Photodesorption of N 2 O from Si-OH sites
    3. Qualitative comparison of gas phase and surface phase photodecomposition of N 2 O
    4. Quantitative measurement of the photochemical rates by infrared spectroscopy
    5. Quantum efficiency of N 2 O photodecomposition on high area SiO 2
  4. DISCUSSION
    1. Efficiency of complex molecule formation from Lyman-α photodecomposition of N 2 O
    2. Decreasing combination reaction rates as photodecomposition increases
    3. The role of the SiO 2 surface on the rate of combination reactions
  5. SUMMARY OF RESULTS

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KEYWORDS and PACS

Keywords

astrochemistry, interstellar matter

PACS

  • 95.30.Ft

    Molecular and chemical processes and interactions

  • 98.58.-w

    Interstellar medium (ISM) and nebulae in external galaxies

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.3532089

PUBLICATION DATA

ISSN

0021-9606 (print)  
1089-7690 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

For access to fully linked references, you need to log in.
    M. Zelikoff, K. Watanabe, and E. C. Y. Inn, J. Chem. Phys. 21, 1643 (1953)JCPSA6000021000010001643000001.

    N. R. Greiner, J. Chem. Phys. 47, 4373 (1967)JCPSA6000047000011004373000001.

    G. Black, R. L. Sharpless, T. G. Slanger, and D. C. Lorents, J. Chem. Phys. 62, 4266 (1975)JCPSA6000062000011004266000001.

    H. M. Lambert, E. W. Davis, O. Tokel, A. A. Dixit, and P. L. Houston, J. Chem. Phys. 122, 174304 (2005)JCPSA6000122000017174304000001.

    H. Okabe, J Chem. Phys. 47, 101 (1967)JCPSA6000047000001000101000001.

    E. Herbst, J. Chem. Phys. 70, 2201 (1979)JCPSA6000070000005002201000001.


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