Near-UV photolysis cross sections of CH3OOH and HOCH2OOH determined via action spectroscopy
1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
2Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125, USA
3Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125, USA
*now at: Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
**now at: Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720-1460, USA
Abstract. Knowledge of molecular photolysis cross sections is important for determining atmospheric lifetimes and fates of many species. A method and laser apparatus for measurement of these cross sections in the near-ultraviolet (UV) region is described. The technique is based on action spectroscopy, where the yield of a photodissociation product (in this case OH) is measured as a function of excitation energy. For compounds yielding OH, this method can be used to measure near-UV photodissociation cross section as low as 10−23 cm2 molecule−1. The method is applied to determine the photodissociation cross sections for methyl hydroperoxide (CH3OOH; MHP) and hydroxymethyl hydroperoxide (HOCH2OOH; HMHP) in the 305–365 nm wavelength range. The measured cross sections are in good agreement with previous measurements of absorption cross sections.