X-Ray Photoelectron Spectroscopy and Mass Spectrometry Studies of X-Ray-processed Solid CO_2

Details X-Ray Photoelectron Spectroscopy and Mass Spectrometry Studies of X-Ray-processed Solid CO_2 X-Ray Photoelectron Spectroscopy and Mass Spectrometry Studies of X-Ray-processed Solid CO_2

Sep 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...505..443c&link_type=abstract

The Astrophysical Journal, Volume 505, Issue 1, pp. 443-451.

Astronomy and Astrophysics

Astronomy

4

Diffusion, Ism: Molecules, Molecular Processes, X-Rays: General

Scientific paper

Solid CO_2 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 CO_2 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 H_2CO, CH_3OH, and a water ice cap on the CO_2 film. The rate of production of CO from direct X-ray photolysis of CO_2 is measured to be 5.4 x 10^2 molecule photon^-1, corresponding to a formation cross section of 4.7 x 10^-20 cm^2. The growth rate for the water cap is calculated to be 2.6 x 10^-4 monolayers s^-1 for a partial pressure of H equal to 2 x 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 CO_2 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 CO_2 of 5 x 10^-12 and 1 x 10^-12 cm^2 s^-1, for O and CO, respectively.

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