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Science 19 June 2009:
Vol. 324. no. 5934, p. 1516
DOI: 10.1126/science.1167717
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Technical Comments

Comment on "Experimental Test of Self-Shielding in Vacuum Ultraviolet Photodissociation of CO"

James R. Lyons,1,* Roy S. Lewis,2 Robert N. Clayton3

Chakraborty et al. (Reports, 5 September 2008, p. 1328) demonstrated very large, wavelength-dependent mass-independent isotopic effects during carbon monoxide (CO) photodissociation and argued that self-shielding in CO was not responsible. We suggest that variations in band oscillator strengths and linewidths among CO isotopologs are responsible for most of the wavelength dependence observed and that the reported experiments confirm the importance of self-shielding during CO photodissociation.

1 Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, CA 90095, USA.
2 Enrico Fermi Institute and Chicago Center for Cosmochemistry, University of Chicago, Chicago, IL 60637, USA.
3 Enrico Fermi Institute and Departments of Chemistry and Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA.

* To whom correspondence should be addressed. E-mail: jimlyons{at}ucla.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)