Negative-Ion Photoelectron Spectroscopy, Gas-Phase Acidity, and Thermochemistry of the Peroxyl Radicals CH3OO and CH3CH2OO

S. J. Blanksby, T. M. Ramond, G. E. Davico, M. R. Nimlos, S. Kato, V. M. Bierbaum, W. C. Lineberger, G. B. Ellison, M. Okumura

Research output: Contribution to journalArticlepeer-review

138 Scopus Citations


Methyl, methyl-d3, and ethyl hydroperoxide anions (CH3OO-, CD3OO-, and CH3CH2OO-) have been prepared by deprotonation of their respective hydroperoxides in a stream of helium buffer gas. Photodetachment with 364 nm (3.408 eV) radiation was used to measure the adiabatic electron affinities: EA[CH3OO, X̃ 2A″]=1.161±0.005 eV, EA[CD3OO, X̃ 2A″]=1.154±0.004 eV, and EA[CH3CH2OO, X̃ 2A″]=1.186±0.004 eV. The photoelectron spectra yield values for the term energies: ΔE(X̃ 2A″-Ã 2A′)-[CH3OO]=0.914±0.005 eV, ΔE(X̃ 2A″-Ã 2A′)[CD3OO]=0.913±0.004 eV, and ΔE(X̃ 2A″-Ã 2A′)-[CH3CH2OO]=0.938±0.004 eV. A localized RO-O stretching mode was observed near 1100 cm-1for the ground state of all three radicals, and low-frequency R-O-O bending modes are also reported. Proton-transfer kinetics of the hydroperoxides have been measured in a tandem flowing afterglow-selected ion flow tube (FA-SIFT) to determine the gas-phase acidity of the parent hydroperoxides: ΔacidG298(CH3OOH)=367.6±0.7 kcal mol-1, ΔacidG298(CD3OOH)=367.9±0.9 kcal mol-1, and ΔacidG298(CH3CH 2OOH)=363.9±2.0 kcal mol-1. From these acidities we have derived the enthalpies of deprotonation: ΔacidH298(CH3OOH)=374.6±1.0 kcal mol-1, ΔacidH298(CD3OOH)=374.9 1.1 kcal mol-1, and ΔacidH298(CH3CH 2OOH)=371.0±2.2 kcal mol-1. Use of the negative-ion acidity/EA cycle provides the ROO-H bond enthalpies: DH298(CH3OO-H)=87.8±1.0 kcal mol-1, DH298(CD3OO-H)=87.9±1.1 kcal mol-1, and DH298(CH3-CH2OO-H)=84.8±2.2 kcal mol-1. We review the thermochemistry of the peroxyl radicals, CH3OO and CH3CH2OO. Using experimental bond enthalpies, DH298(ROO-H), and CBS/APNO ab initio electronic structure calculations for the energies of the corresponding hydroperoxides, we derive the heats of formation of the peroxyl radicals. The "electron affinity/acidity/CBS" cycle yields ΔfH298[CH3OO]=4.8±1.2 kcal mol-1 and ΔfH298[CH3CH 2OO]=-6.8±2.3 kcal mol-1.

Original languageAmerican English
Pages (from-to)9585-9596
Number of pages12
JournalJournal of the American Chemical Society
Issue number39
StatePublished - 2001

NREL Publication Number

  • NREL/JA-510-31278


Dive into the research topics of 'Negative-Ion Photoelectron Spectroscopy, Gas-Phase Acidity, and Thermochemistry of the Peroxyl Radicals CH3OO and CH3CH2OO'. Together they form a unique fingerprint.

Cite this