The 351.1 nm photoelectron spectrum of the peroxyacetate anion, (CH₃C(O)OO⁻) was measured. Analysis of the spectrum shows that the observed spectral features arise almost exclusively from transitions between the trans-conformer of the anion and the X˜²₂A″ and Ã²A′ states of the corresponding radical. The electron affinity of trans-CH₃C(O)OO is 2.381 ± 0.007 eV and the term energy splitting of the Ã²A′ state is 0.691 ± 0.009 eV, in excellent agreement with two prior values [Zalyubovsky et al. J. Phys. Chem. A 107, 7704 (2003); Hu et al. J. Phys. Chem. 124, 114305/1 (2006); Hu et al. J. Phys. Chem. 110, 2629 (2006)]. The gas-phase acidity of trans-peroxyacetic acid was bracketed between the acidity of acetic acid and tert-butylthiol at Δ_aG₂₉₈(trans-CH₃C(O)OOH) = 1439 ± 14 kJ mol⁻¹ and Δ_aH₂₉₈(trans-CH₃C(O) OOH) = 1467 ± 14 kJ mol⁻¹. The acidity of cis-CH₃C(O)OOH was found by adding a calculated energy correction to the acidity of the trans-conformer; Δ_aG₂₉₈[cis-CH₃C(O)OOH] = 1461 ± 14 kJ mol⁻¹ and Δ_aH₂₉₈[cis-CH₃C(O)OOH] = 1490 ± 14 kJ mol⁻¹. The O–H bond dissociation energies for both conformers were determined using a negative ion thermodynamic cycle to be D₀[trans-CH₃C(O)OOH] = 381 ± 14 kJ mol⁻¹ and D₀[cis-CH₃C(O)OOH] = 403±14 kJ mol⁻¹. The atmospheric implications of these results and relations to the thermochemistry of peroxyacetyl nitrate are discussed briefly.

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Photoelectron Spectroscopy and Thermochemistry of the Peroxyacetate Anion