X-ray photoelectron spectroscopy and mass spectrometry studies of X-ray-processed solid CO2

D. M. Cornelison, T. R. Dillingham, S. C. Tegler, K. Galle, G. A. Miller, B. L. Lutz

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

Solid CO2 films have been grown on a stainless steel substrate and processed by X-ray bombardment for up to 6 hr.. The reactions induced were monitored using X-ray photoelectron spectroscopy (XPS) and mass spectrometry. The XPS results are twofold: direct X-ray photolysis of the CO2 ice produced CO and an unidentified O product, possibly atomic O; secondary effects resulting from surface reactions between CO, O, and residual H from the vacuum environment produced H2CO, CH3OH, and a water ice cap on the CO2 film. The rate of production of CO from direct X-ray photolysis of CO2 is measured to be 5.4 × 102 molecule photon-1, corresponding to a formation cross section of 4.7 × 10-20 cm2. The growth rate for the water cap is calculated to be 2.6 × 10-4 monolayers s-1 for a partial pressure of H equal to 2 × 10-10 Torr. The appearance of gas-phase products from the film showed a time lag which indicates that the diffusion of the product species in the bulk CO2 is affected by some time-dependent process, possibly the creation of defects in the film. A model for the observed time dependence of the dissociation products in the gas phase yields diffusion coefficients in the CO2 of 5 × 10-12 and 1 × 10-12 cm2 s-1, for O and CO, respectively.

Original languageEnglish (US)
Pages (from-to)443-451
Number of pages9
JournalAstrophysical Journal
Volume505
Issue number1 PART I
DOIs
StatePublished - Jan 1 1998

Keywords

  • Diffusion
  • ISM: molecules
  • Molecular processes
  • X-rays: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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