TY - JOUR
T1 - Radical quantum yields from formaldehyde photolysis in the 30 400-32 890 cm-1 (304-329 nm) spectral region
T2 - Detection of radical photoproducts using pulsed laser photolysis-pulsed laser induced fluorescence
AU - Tatum Ernest, Cheryl
AU - Bauer, Dieter
AU - Hynes, Anthony J.
PY - 2012/7/5
Y1 - 2012/7/5
N2 - The relative quantum yield for the production of radical products, H + HCO, from the UV photolysis of formaldehyde (HCHO) has been measured using a pulsed laser photolysis-pulsed laser induced fluorescence (PLP-PLIF) technique across the 30 400-32 890 cm-1 (304-329 nm) spectral region of the Ã1A2-X̃1A1 electronic transition. The photolysis laser had a bandwidth of ∼0.09 cm-1, which is slightly broader than the Doppler width of a rotational line of formaldehyde at 300 K (∼0.07 cm-1), and the yield spectrum shows detailed rotational structure. The H and HCO photofragments were monitored using LIF of the OH radical as a spectroscopic marker. The OH radicals were produced by rapid reaction of the H and HCO photofragments with NO2. This technique produced an "action" spectrum that at any photolysis wavelength is the product of the H + HCO radical quantum yield and HCHO absorption cross section at the photolysis wavelength and is a relative measurement. Using the HCHO absorption cross section previously obtained in this laboratory, the relative quantum yield was determined two different ways. One produced band specific yields, and the other produced yields averaged over each 100 cm-1. Yields were normalized to a value of 0.69 at 31 750 cm -1 based on the current recommendation of Sander et al. (Sander, S. P.; Abbatt, J.; Barker, J. R.; Burkholder, J. B.; Friedl, R. R.; Golden, D. M.; Huie, R. E.; Kolb, C. E.; Kurylo, M. J.; Moortgat, G. K.; et al. Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies, Evaluation No. 17; Jet Propulsion Laboratory: Pasadena, CA, USA, 2011). The resulting radical quantum yields agree well with previous experimental studies and the current JPL recommendation but show greater wavelength dependent structure. A significant decrease in the quantum yield was observed for the 501 + 10 1401 combination band centered at 31 125 cm-1. This band has a low absorption cross section and has little impact on the calculated atmospheric photodissociation rate but is a further indication of the complexity of HCHO photodissociation dynamics.
AB - The relative quantum yield for the production of radical products, H + HCO, from the UV photolysis of formaldehyde (HCHO) has been measured using a pulsed laser photolysis-pulsed laser induced fluorescence (PLP-PLIF) technique across the 30 400-32 890 cm-1 (304-329 nm) spectral region of the Ã1A2-X̃1A1 electronic transition. The photolysis laser had a bandwidth of ∼0.09 cm-1, which is slightly broader than the Doppler width of a rotational line of formaldehyde at 300 K (∼0.07 cm-1), and the yield spectrum shows detailed rotational structure. The H and HCO photofragments were monitored using LIF of the OH radical as a spectroscopic marker. The OH radicals were produced by rapid reaction of the H and HCO photofragments with NO2. This technique produced an "action" spectrum that at any photolysis wavelength is the product of the H + HCO radical quantum yield and HCHO absorption cross section at the photolysis wavelength and is a relative measurement. Using the HCHO absorption cross section previously obtained in this laboratory, the relative quantum yield was determined two different ways. One produced band specific yields, and the other produced yields averaged over each 100 cm-1. Yields were normalized to a value of 0.69 at 31 750 cm -1 based on the current recommendation of Sander et al. (Sander, S. P.; Abbatt, J.; Barker, J. R.; Burkholder, J. B.; Friedl, R. R.; Golden, D. M.; Huie, R. E.; Kolb, C. E.; Kurylo, M. J.; Moortgat, G. K.; et al. Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies, Evaluation No. 17; Jet Propulsion Laboratory: Pasadena, CA, USA, 2011). The resulting radical quantum yields agree well with previous experimental studies and the current JPL recommendation but show greater wavelength dependent structure. A significant decrease in the quantum yield was observed for the 501 + 10 1401 combination band centered at 31 125 cm-1. This band has a low absorption cross section and has little impact on the calculated atmospheric photodissociation rate but is a further indication of the complexity of HCHO photodissociation dynamics.
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U2 - 10.1021/jp2117399
DO - 10.1021/jp2117399
M3 - Article
C2 - 22625180
AN - SCOPUS:84863613175
VL - 116
SP - 6983
EP - 6995
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
SN - 1089-5639
IS - 26
ER -