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Volumn 302, Issue 5652, 2003, Pages 1943-1946

Importance of Surface Morphology in Interstellar H2 Formation

Author keywords

[No Author keywords available]

Indexed keywords

MORPHOLOGY; SURFACES; THIN FILMS;

EID: 0347504728     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.1090820     Document Type: Article
Times cited : (162)

References (26)
  • 11
    • 0347905992 scopus 로고    scopus 로고
    • note
    • 2O deposition conditions are typically ∼45° HWHM angular spread and 0.3 to 3 ML/s dose rates.
  • 13
    • 0346014594 scopus 로고    scopus 로고
    • note
    • 2-1-, beam dissociation probabilities of ∼65%, and Maxwell-Boltzmann kinetic energy distributions of T = 300 K. The H and D beams are incident upon the ASW surface at 0° and 4° relative to the surface normal and are overlapped at the center of the ASW surface with beam diameters of 1.5 mm and 3.5 mm, respectively.
  • 14
    • 0346014596 scopus 로고    scopus 로고
    • note
    • 2 from the front of the ASW surface with a differentially pumped quadrupole mass spectrometer (QM5) with an aperture close to the ASW surface to limit the field of view in the TPD. LITD measurements were performed by inducing a temperature jump of typically 20 ns on the surface using a 200 μJ laser pulse at 532 nm focused to a 1.5 mm diameter spot at the center of the overlapped atom beams. The kinetic energy distribution of molecules desorbing during the temperature jump are obtained from the TOF distributions to another differentially pumped mass spectrometer placed 10 cm from the surface (21).
  • 16
    • 0346014593 scopus 로고    scopus 로고
    • note
    • The desorption yield and TPD spectra for HD were unaffected by repeated cycling of H+D adsorption experiments on the same ASW film, indicating that little restructuring of the ASW pore structure takes place as a result of the release of the recombination energy. Hence, the retainment of HD molecules in ASW pores is not caused by pore collapse and volcano formation, as seen for more tightly bound adsorbates exhibiting rapid low-temperature thermal diffusion (25), but is simply due to the fact that particles describing from pore surfaces in the porous network have to undergo a series of adsorption-desorption cycles before making their way to the external film surface, from which desorption into the gas phase can take place.
  • 17
    • 0346645785 scopus 로고    scopus 로고
    • note
    • The distinction between the Langmuir-Hinshelwood (LH) and hot atom reaction mechanisms is in the origin of atom mobility on the 10 K surface. In the LH mechanism, this is caused by thermal atom diffusion, whereas in the hot atom mechanism this is caused by transient mobility on the surface during the adsorption process, i.e., before the atom fully thermalizes on the surface. All experiments reported here are consistent with both mechanisms. Our bias is that the LH mechanism dominates because of the absence of H coverage dependence in apparent rates of recombination and because it is hard to rationalize HD retention in the internal porous surface if hot atom reaction occurs on the external surface.
  • 18
    • 0346014592 scopus 로고    scopus 로고
    • note
    • The small residual signal in Fig. 2 is thought to arise from recombination of atoms trapped at the Cusubstrate-ASW interface.
  • 19
    • 0346014591 scopus 로고    scopus 로고
    • note
    • s ∼ 8 K, as obtained by the King and Wells method.
  • 26
    • 0346645783 scopus 로고    scopus 로고
    • note
    • Supported by The Danish National Research Council (grant no. 21000269), the Danish National Research Foundation through the Aarhus Center of Atomic Physics, and the Carlsberg Foundation. We thank B. Kay and A. Andersen for useful discussions and advice.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.