Gas phase UV absorption spectra for peracetic acid, and for acetic acid monomers and dimers

Absorption cross sections have been determined in the UV spectral region (205–350 nm) for gas phase acetic acid (CH3C(O)OH) in its monomeric and dimeric forms (270–345 K), as well as for peracetic acid (CH3C(O)OOH, 248 and 298 K). Analysis of acetic acid spectra recorded over a range of pressures (0.12–3.6 Torr), coupled with a prior knowledge of the dimerization equilibrium constant, allowed for the deconvolution of the monomer and dimer absorption spectra. The 298 K monomer spectrum consists of a maximum near 207 nm (σ=1.4×10−19 cm2 per molecule), with monotonically decreasing cross sections at longer wavelengths. The dimer spectrum possesses a maximum located short of 205 nm, with a peak intensity about double that of the monomer. The first gas phase spectrum of peracetic acid is also reported, which is similar to a previously published solution-phase spectrum. Measurable absorption extends to 340 nm at 298 K, and it is determined that the tropospheric photolysis of this species will be a reasonably rapid process (lifetime ≈ weeks), which will play at least a minor role in its atmospheric destruction.