The 364 nm negative ion photoelectron spectra of CF2 -, CCl2 -, CBr2 -, and CI2 - exhibit transitions to two different electronic states, the 1A1 and 3B1. The CF2 - spectrum exhibits well-resolved transitions to both electronic states. In the cases of CCl2 -, CBr2 -, and CI2 -, the spectra exhibit extended, partially resolved vibrational progressions and the two states are overlapped, making a direct determination of the origin transition energy not possible. The overlapped spectra show that the singlet−triplet splittings in the heavier halocarbenes are much smaller than for CF2 -. The results of ab initio calculations have been used to generate Franck−Condon simulations of the spectra, which aid in the determination of the band origins. The 1A1 state is found to be the lower state for CF2, CCl2, and CBr2 and the electron affinities have been determined to be 0.180 ± 0.020, 1.59 ± 0.07, and 1.88 ± 0.07 eV, respectively. For CI2, the triplet state is apparently the lower lying state with an electron affinity of 2.09 ± 0.07 eV. The singlet−triplet splitting energy has been determined to be 54 ± 3, 3 ± 3, 2 ± 3, −1 ± 3 kcal/mol for CF2, CCl2, CBr2, and CI2, respectively. In addition, the bending and symmetric stretching vibrational frequencies have been determined for either one or both states.

Ultraviolet photoelectron spectra of CH 3 O Ϫ , CH 3 CH 2 O Ϫ , (CH 3) 2 CHO Ϫ , (CH 3) 3 CO Ϫ , as well as CD 3 O Ϫ and CD 3 CD 2 O Ϫ are presented, providing improved electron affinities and new information on vibronic coupling in the corresponding neutral radicals. Jahn-Teller vibronic transitions are assigned to e vibrational modes of X 2 E CH 3 O. The excitation energy of the à 2 AЈ state of CH 3 CH 2 O with respect to the X 2 AЉ state is observed directly at 355Ϯ10 cm Ϫ1. Vibronic coupling between these low-lying electronic states perturbs the observed vibronic levels. Features of the (CH 3) 2 CHO Ϫ photoelectron spectrum are assigned. The splitting between the X 2 AЈ and à 2 AЉ states of (CH 3) 2 CHO is determined to be 1225Ϯ65 cm Ϫ1. Significant vibronic coupling is not observed in (CH 3) 2 CHO. Vibrational assignments are made for the spectral features of (CH 3) 3 CO and no Jahn-Teller effects are observed directly. Electron affinities ͑EAs͒ for the neutrals ͑RO͒ are ͑in eV͒; EA͑CH 3 O͒ϭ1.572Ϯ0.004; EA͑CD 3 O͒ϭ1.559Ϯ0.004; EA͑CH 3 CH 2 O)ϭ1.712Ϯ0.004; EA͑CD 3 CD 2 O)ϭ1.699Ϯ0.004; EA͑͑CH 3) 2 CHO)ϭ1.847Ϯ0.004; EA͑͑CH 3) 3 CO)ϭ1.909 Ϯ0.004. Bond dissociation energies of ROH, D 300 ͑RO-H͒, along with ⌬ f H 300 ͑RO͒, ⌬ f H 300 ͑RO Ϫ), and ⌬ f H 300 ͑RO ϩ) are derived.

Methyl, methyl-d(3), and ethyl hydroperoxide anions (CH(3)OO(-), CD(3)OO(-), and CH(3)CH(2)OO(-)) 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[CH(3)OO, X(2)A' '] = 1.161 +/- 0.005 eV, EA[CD(3)OO, X(2)A' '] = 1.154 +/- 0.004 eV, and EA[CH(3)CH(2)OO, X(2)A' '] = 1.186 +/- 0.004 eV. The photoelectron spectra yield values for the term energies: Delta E(X(2)A' '-A (2)A')[CH(3)OO] = 0.914 +/- 0.005 eV, Delta E(X(2)A' '-A (2)A')[CD(3)OO] = 0.913 +/- 0.004 eV, and Delta E(X(2)A' '-A (2)A')[CH(3)CH(2)OO] = 0.938 +/- 0.004 eV. A localized RO-O stretching mode was observed near 1100 cm(-1) for 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: Delta(acid)G(298)(CH(3)OOH) = 367.6 +/- 0.7 kcal mol(-1), Delta(acid)G(298)(CD(3)OOH) = 367.9 +/- 0.9 kcal mol(-1), and Delta(acid)G(298)(CH(3)CH(2)OOH) = 363.9 +/- 2.0 kcal mol(-1). From these acidities we have derived the enthalpies of deprotonation: Delta(acid)H(298)(CH(3)OOH) = 374.6 +/- 1.0 kcal mol(-1), Delta(acid)H(298)(CD(3)OOH) = 374.9 +/- 1.1 kcal mol(-1), and Delta(acid)H(298)(CH(3)CH(2)OOH) = 371.0 +/- 2.2 kcal mol(-1). Use of the negative-ion acidity/EA cycle provides the ROO-H bond enthalpies: DH(298)(CH(3)OO-H) = 87.8 +/- 1.0 kcal mol(-1), DH(298)(CD(3)OO-H) = 87.9 +/- 1.1 kcal mol(-1), and DH(298)(CH(3)CH(2)OO-H) = 84.8 +/- 2.2 kcal mol(-1). We review the thermochemistry of the peroxyl radicals, CH(3)OO and CH(3)CH(2)OO. Using experimental bond enthalpies, DH(298)(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 Delta(f)H(298)[CH(3)OO] = 4.8 +/- 1.2 kcal mol(-1) and Delta(f)H(298)[CH(3)CH(2)OO] = -6.8 +/- 2.3 kcal mol(-1).