Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 4 2 2004 10.5194/acpd-4-1269-2004 http://www.atmos-chem-phys-discuss.net/4/1269/2004/ http://www.atmos-chem-phys-discuss.net/4/1269/2004/acpd-4-1269-2004.html http://www.atmos-chem-phys-discuss.net/4/1269/2004/acpd-4-1269-2004.pdf 1269 1289 2004-03-01 Near-IR photodissociation of peroxy acetyl nitrate S. A. Nizkorodov nizkorod@uci.edu J. D. Crounse J. L. Fry C. M. Roehl P. O. Wennberg Department of Chemistry, University of California at Irvine, Irvine, CA 92697, USA Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA Division of Geological and Planetary Sciences and Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA, 91125, USA Measurements of the C-H overtone transition strengths combined with estimates of the photodissociation cross sections for these transitions suggest that near-IR photodissociation of peroxy acetyl nitrate (PAN) is less significant (Jnear-IR≈3×10−8s−1 at noon) in the lower atmosphere than competing sinks resulting from unimolecular decomposition and ultraviolet photolysis. This is in contrast to the photochemical behavior of a related peroxy nitrate, pernitric acid (PNA), that undergoes rapid near-IR photolysis in the atmosphere with Jnear-IR≈10−5s−1 at noon (Roehl et al., 2002). This difference is attributed to the larger binding energy and larger number of vibrational degrees of freedom in PAN, which make 4νCH the lowest overtone excitation with a high photodissociation yield (as opposed to 2νOH in PNA).