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 (CH ₃ C(O)OH) in its monomeric and dimeric forms (270-345 K), as well as for peracetic acid (CH ₃ C(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 cm ² 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.