Phototautomerization of Acetaldehyde to Vinyl Alcohol: A Primary Process in UV-Irradiated Acetaldehyde from 295 to 335 nm.
The concentrations of organic acids, key species in the formation of secondary organic aerosols, are underestimated by atmospheric chemistry models by a factor of ∼2. Vinyl alcohol (VA, CH2═CHOH, ethenol) has been suggested as a precursor to formic acid, but sufficient tropospheric sources of VA have not been identified. Here, we show that VA is formed upon irradiation of neat acetaldehyde (CH3CHO) in the actinic ultraviolet region, between 295 and 330 nm. Besides the well-known photochemical products CO and CH4, we infer up to a 15% quantum yield of VA at 20 Torr acetaldehyde pressure and a photolysis wavelength of 330 nm. The experiments confirm a recent model predicting phototautomerization of acetaldehyde to VA and imply that photolysis of small aldehydes and ketones could provide tropospheric sources of enols sufficient to impact organic acid budgets. We also report absolute infrared absorption cross sections of VA.
School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia.|Combustion Research Facility, Sandia National Laboratories, PO Box 969, MS 9055 Livermore, California 94551-0969, United States.
Alexander E
AE
Clubb
School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia.|Combustion Research Facility, Sandia National Laboratories, PO Box 969, MS 9055 Livermore, California 94551-0969, United States.
Meredith J T
MJ
Jordan
School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia.|Combustion Research Facility, Sandia National Laboratories, PO Box 969, MS 9055 Livermore, California 94551-0969, United States.
S H
SH
Kable
School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia.|Combustion Research Facility, Sandia National Laboratories, PO Box 969, MS 9055 Livermore, California 94551-0969, United States.
David L
DL
Osborn
FTIR spectroscopy; IR absorption cross section; atmospheric chemistry; isomerization; kinetics; photochemistry; tautomerization