The photoelectron spectrum of vinoxide, C2H3O-, at 355 nm is reported, showing photodetachment to both the X(2A‘ ‘) ground and first excited A(2A‘) states of the vinoxy radical. Both direct interpretations and Franck−Condon simulations of the photoelectron spectrum of this simple enolate anion have been used to obtain insights into the energetics and structures of the anion and the ground and first excited state of the neutral radical. Franck−Condon simulations were generated from ab initio geometry and frequency calculations using the CASSCF method and showed good agreement with the vibrational structure visible in the experimental spectrum. The electron affinity (E.A.exp = 1.795 ± 0.015 eV; E.A.calc = 1.82 eV) and separation energy of the ground and first excited states (T 0,exp = 1.015 ± 0.015 eV; T 0,calc = 0.92 eV) obtained from the ab initio calculations are in good accord with the experimental values.

The self-reactions and cross reactions of the peroxy radicals C2H5O2 and HO2 were monitored using simultaneous independent spectroscopic probes to observe each radical species. Wavelength modulation (WM) near-infrared (NIR) spectroscopy was used to detect HO2, and UV absorption monitored C2H5O2. The temperature dependences of these reactions were investigated over a range of interest to tropospheric chemistry, 221-296 K. The Arrhenius expression determined for the cross reaction, k2(T) = (6.01(-1.47)(+1.95)) x 10(-13) exp((638 +/- 73)/T) cm3 molecules(-1) s(-1) is in agreement with other work from the literature. The measurements of the HO2 self-reaction agreed with previous work from this lab and were not further refined. The C2H5O2 self-reaction is complicated by secondary production of HO2. This experiment performed the first direct measurement of the self-reaction rate constant, as well as the branching fraction to the radical channel, in part by measurement of the secondary HO2. The Arrhenius expression for the self-reaction rate constant is k3(T) = (1.29(-0.27)(+0.34)) x 10(-13)exp((-23 +/- 61)/T) cm3 molecules(-1) s(-1), and the branching fraction value is alpha = 0.28 +/- 0.06, independent of temperature. These values are in disagreement with previous measurements based on end product studies of the branching fraction. The results suggest that better characterization of the products from RO2 self-reactions are required.

The photoelectron spectra of the structural isomers of the three- and four-carbon enolate anions, n-C3H5O(-), i-C3H5O(-), n-C4H7O(-), s-C4H7O(-), and i-C4H7O(-) have been measured at 355 nm. Both the X(2A' ') ground and A(2A') first excited states of the corresponding radicals were accessed from the X(1A') ground state of the enolate anions. The separation energies of the ground and first excited states (T0) were determined: T0[(E)-n-C3H5O] = 1.19 +/- 0.02 eV, T0[(Z)-n-C3H5O] = 0.99 +/- 0.02 eV, T0[i-C3H5O] = 1.01 +/- 0.02 eV, T0[n-C4H7O] = 1.19 +/- 0.02 eV, T0[(2,3)-s-C4H7O] = 1.25 +/- 0.02 eV, T0[(1,2)-s-C4H7O] = 0.98 +/- 0.02 eV, and T0[i-C4H7O] = 1.36 +/- 0.02 eV. The effects of alkyl substitution on the vibronic structure and energetics previously observed in the vinoxy radical are discussed. The X(1A')-X(2A' ') relative stability is strongly influenced by substitution whereas the X(1A')-A(2A') relative stability remains nearly constant for all of the observed structural isomers. Alkyl substitution at the carbonyl carbon affects vibronic structure more profoundly than the energetics, while the converse is observed upon alkyl substitution at the alpha carbon.

The photoelectron spectra of the trifluoromethyl anion, CF3 -, at 355 and 258 nm are reported. Simulation of the partially resolved vibrational structure is used to extract the adiabatic electron affinity, AEA[CF3] = 1.82 ± 0.05 eV. The heat of formation for the trifluoromethyl anion derived from the adiabatic electron affinity (Δ [CF3 -] = −153.4 ± 1.5 kcal/mol) is compared to the high-accuracy “isodesmic bond additivity corrected” (BAC) complete basis set (CBS-Q) theory prediction (Δ [CF3 -] = −152.6 kcal/mol). We find the CBS-Q prediction of Δ [CF3] = −112.1 kcal/mol, after BAC, to be in excellent agreement with the most recent experimental determination of the radical heat of formation. The photoelectron angular distribution at 355 nm was also extracted from the photoelectron image, revealing p wave photodetachment with an energy-averaged anisotropy parameter of β = 1.5 ± 0.1.

Photoelectron spectra of SO3 - were recorded at 266 and 355 nm to study photodetachment of the SO3 - anion (2A1) to the ground state of neutral SO3 (1A‘1). A long vibrational progression in the 355 nm spectrum is attributed to excitation of the umbrella mode, ν2, consistent with predictions that C 3 v symmetry SO3 - yields D 3 h symmetry SO3 upon photodetachment. At 266 nm, photodissociation of SO3 - to SO2 + O- was also observed. The geometry and normal-mode frequencies of SO3 - and SO3 as well as the adiabatic electron affinity (AEA) and vertical detachment energy (VDE) of SO3 have also been calculated with ab initio (MP2 and CCSD(T)) and DFT methods. Using theoretical predictions and experimental data, Franck−Condon simulations of the photoelectron spectra were found to be in good agreement with experiment. The calculated AEA agreed well with experiment, but the VDE was found to be less accurate, presumably because of the large geometry change between anion and neutral.