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Volume 130, 2005
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Photochemistry of formaldehyde under tropospheric conditions

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Abstract

We report new results on the absorption cross sections and photochemical quantum yields for radical (H + HCO) production from formaldehyde in the wavelength interval from 308–320 nm, obtained at resolutions of better than 0.1 nm. The absorption cross sections, measured at resolutions close to the limit for Doppler broadening of HCHO, show rotationally resolved fine structure, with maximum values higher than those obtained in previous, lower resolution, studies. In this wavelength region, absorption cross sections peak at 2.3 × 10−19 cm2 molecule−1, but band-integrated values are in excellent accord with previous measurements. HCO absorption coefficients, measured by cavity ring-down spectroscopy following UV photolysis of HCHO at wavelengths across the 210510, 220430 and 230410 bands of the Ã1A2[X with combining tilde]1A1 transition, generally mimic the parent absorption band profiles. Division of these absorption coefficients by the high resolution parent absorption cross sections gives relative quantum yields for the H + HCO radical product channel that can be put on an absolute scale using single-wavelength literature values. These quantum yields are observed to show some variation with parent excitation wavelength (and thus with excited vibronic level). Addition of 200 Torr of N2 increases the HCO quantum yields.

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Publication details

The article was received on 22 Dec 2004, accepted on 04 Feb 2005 and first published on 22 Apr 2005


Article type: Paper
DOI: 10.1039/B419227C
Citation: Faraday Discuss., 2005,130, 59-72
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    Photochemistry of formaldehyde under tropospheric conditions

    F. D. Pope, C. A. Smith, P. R. Davis, D. E. Shallcross, M. N. R. Ashfold and A. J. Orr-Ewing, Faraday Discuss., 2005, 130, 59
    DOI: 10.1039/B419227C

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