G. B. Ellison

Laser photodetachment electron spectrometry of methoxide, deuteromethoxide, and thiomethoxide: Electron affinities and vibrational structure of CH30, CD30, and CH3S

Photodetachment of the three anions CH3O−, CD3O−, and CH3S− by a fixed‐frequency argon ion laser at 488 nm and subsequent energy analysis of the photoelectrons yields the photoelectron spectra of these species. From the spectra, electron affinities were determined: E.A.(CH3O) = (1.570±0.022) eV, E.A.(CD3O) = (1.552±0.022) eV, E.A.(CH3S) = (1.882±0.024) eV. From the vibrational structure appearing in the spectra, and the shifts observed upon deuteration, the predominant motion excited in the neutral upon photodetachment of CH3O− and CD3O− is found to be the symmetric hydrogen umbrella bend at 1325±30 and 1010±30 cm−1, respectively. In CH3S both the symmetric hydrogen bend and the carbon–sulfur bond stretch (680±40 cm−1) are excited. From the observed hot bands, some vibrational frequencies of the negative ions are also derived.

Laser photoelectron spectroscopy of CH2−, and the singlet–triplet splitting in methylene

Photodetachment of an electron from CH2− ions using visible light produces CH2 in both its ground 3B1 and lowest excited 1A1 states. In an earlier letter, this process was utilized to determine directly a singlet–triplet splitting of 19.5 kcal/mol. In this paper are reported the details of the early measurement and a number of additional investigations designed to test critically the earlier assignments. Data reported here indicate that one suggested problem with the early results, a misassignment of the 3B1 origin resulting from negative ion hot bands, is not likely. These new results do reveal the presence of an additional peak in the photoelectron spectrum which could possibly be the lowest level of the 3B1 state, allowing a singlet–triplet splitting of 19.5 or 23.2 kcal/mol. The results reported here do not indicate any other inconsistency in the original assignment. Finally, these data are discussed in light of the formidable body of theoretical and indirect thermochemical determinations suggesting a...

NH2 electron affinity

The 363.8 nm (3.408 eV) photoelectron spectrum of the NH2 (X 2B1)+e−←NH−2(X 1A1) transition of the amide anion is reported. The electron affinity of amidogen is found to be EA(NH2) =0.771 ±0.005 eV. P, Q, and R rotational branches are observed in the spectrum; a simple model which accounts for the band structure is presented.

Photoelectron spectroscopy and thermochemistry of the peroxyacetate anion.

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 ΔaG298(trans-CH3C(O)OOH) = 1439 ± 14 kJ mol−1 and ΔaH298(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; ΔaG298[cis-CH3C(O)OOH] = 1461 ± 14 kJ mol−1 and ΔaH298[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.