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Anisotropic electron spin resonance (ESR) spectra are reported for the radical anions of hexafluorocyclopropane (c-C3F6-), octafluorocyclobutane (c-C4F8-), and decafluorocyclopentane (c-C5F10-) generated via ?-irradiation in plastically crystalline tetramethylsilane (TMS) and rigid 2-methyltetrahydrofuran (MTHF) matrices. By combining the analysis of these experimental ESR spectra involving anisotropic hyperfine (hf) couplings with a series of quantum chemical computations, the geometrical and electronic structure of these unusual perfluorocycloalkane radical anions have been characterized more fully than in previous studies that considered only the isotropic couplings. Unrestricted Hartree-Fock (UHF) computations with the 6-311+G(d,p) basis set predict planar ring structures for all three radical anions, the ground electronic states being 2A2? for c-C3F6- (D3h symmetry), 2A2u for c-C4F8- (D 4h), and 2A2? for c-C5F 10- (D5h), in which the respective six, eight, and ten 19F-atoms are equivalent by symmetry. A successful test of the theoretical computation is indicated by the fact that the isotropic 19F hf couplings computed by the B3LYP method with the 6-311+G(2df,p) basis set for the optimized geometries are in almost perfect agreement with the experimental values: viz., 19.8 mT (exp) vs 19.78 mT (calc) for c-C 3F6-, 14.85 mT (exp) vs 14.84 mT (calc) for c-C4F8-, 11.6 mT (exp) vs 11.65 mT (calc) for c-C5F10-. Consequently, the same computation method has been applied to calculate the almost axially symmetric anisotropic 19F hf couplings for the magnetically equivalent 19F atoms: (-4.90 mT, -4.84 mT, 9.75 mT) for c-C3F6-, (-3.54 mT, -3.48 mT, 7.02 mT) for c-C4F 8-, and (-2.62 mT, -2.56 mT, 5.18 mT) for c-C 5F10-. ESR spectral simulations performed using the computed principal values of the hf couplings and the spatial orientations of the 19F nuclei as input parameters reveal an excellent fit to the experimental anisotropic ESR spectra of c-C3F6-, c-C4F8-, and c-C 5F1

Highly resolved ESR spectra of monomer, dimer and trimer radical cations of coronene (C24H12) were observed at room temperature for a solution of 1,1,1,3,3,3-hexafluoro-2-propan-2-ol (HFP) containing thallium(III) trifluoroacetate as oxidant. The spectra consisting of multiple lines with isotropic 1H-hyperfine splitting (hfs) constants of 0. 0766 mT (24H) and 0.013 mT (6H) were attributable to a mixture of the dimer with the trimer radical cations, (C24H12)2+ and (C24H12)3+. For (C24H12)2+, the 1H-hfs constant agreed well with the reported value, 0.077 mT. However, for (C 24H12)3+, the values were significantly different from the reported ones, 0.117 mT (12H) and 0.020 mT (24H), by Ohya Nishiguchi et al. [H. Ohya-Nishiguchi, H. Ide, N. Hirota, Chem. Phys. Lett. 66 (1979) 581], but rather similar to those reported by Willigen et al. [H. van Willigen, E. De Boer, J.T. Cooper, W.F. Forbes, J. Chem . Phys. 49 (1968) 1190]. In conflict with Willigen's report, however, no ESR line broadening which has been ascribed to a low stationary concentration of (C 24H12)3+ was detected. Based on ab initio MO calculations for benzene as a compact model of C24H 12, the structure of (C24H12)3+ was investigated in terms of the observed 1H-hfs constants. A staggered sandwich C2v structure was suggested being at the "global" minimum for the benzene trimer cation. In the structure, the unpaired electron spin is predominantly localized to the central ring, which is qualitatively in agreement with the previous ESR results of (C 24H12)3+ by Ohya-Nishiguchi et al. In addition, as a "local" minimum, the benzene trimer was indicated to have a slipped sandwich Cs structure, which is less stable by ca. 19 kJ mol-1 than the "global" minimum. In this structure, the unpaired electron spin was nearly equally distributed on both the central and one of the two side C24H12 molecules. The observed 1H-hfs constants were possibly attributable to the (C 24H12)3+ cation with the analogous slipped sandwich Cs

Isotropic and anisotropic ESR spectra were observed for the radical anions of hexafluorocyclobutene (c-C4F6-), octafluorocyclopentene (c-C5F8-) and perfluoro-2-butene (CF3CF=CFCF3-) in ?-irradiated plastically crystalline neopentane, tetramethylsilane (TMS) and TMS-d12 matrices, or the rigid 2-methyltetrahydrofuran (MTHF) matrix. The isotropic spectra of c-C4F6- and c-C5F8- are characterized by three different sets of pairs of 19F nuclei with the isotropic hyperfine (hf) splittings of 15.2 (2F), 6.5 (2F), 1.1 (2F) mT for oC4F 6- and 14.7 (2F), 7.4 (2F), 1.0 (2F) mT for c-C 5F8-. By comparison with the results of ab initio quantum chemical computations, the large triplet 19F hf splittings of ca. 15 mT are assigned to the two fluorines attached to the C=C bond. The UHF, B3LYP and MP2 computations predict that the geometrical structures of the perfluoroalkenes are strongly distorted by one-electron reduction to form their radical anions, c-C3F4-: C2 symmetry (2A state) ? C2v (1A1), c-C4F6-: C 1 (2A) ? C2v (1A1) and c-C5F8-: C1 (2A) ? Cs (1A'). The structural distortion arises from a mixing of the p* and higher-lying s* orbitals at the C=C carbons similar to that previously found for CF2=CF 2- with a C2h, distortion. The isotropic 19F hf splittings computed with the B3LYP method with 6-311+G(2df,p) basis set for the geometry optimized by the UHF and/or MP2 methods are within 6% error of the experimental values. The experimental anisotropic spectra of c-C4F6-, c-C5F8- and CF2=CF2- were satisfactorily reproduced by the ESR spectral simulation method using the computed hf principal values and orientation of 19F nuclei. In addition, the electronic excitation energies and oscillator strengths for the CF2=CF 2-, c-C3F4-, c-C 4F6- and c-C5F8- radical anions were computed for the first time by TD-DFT methods. © 2006 American Chemical Society.

Quantum chemical calculations have been performed on the ground state and several low-lying excited states of bromobenzene, ortho-, meta-, and para-dibromobenzene, and 1,3,5-tribromobenzene using high-level ab initio and hybrid density-functional methods. Experimental observations of ultrafast predissociation in these molecules are clarified from extensive theoretical information about all low-energy potential-energy curves together with symmetry arguments. The intriguing observation that o- and m-dibromobenzene have two ultrafast predissociation channels while bromobenzene, p-dibromobenzene, and 1,3,5-tribromobenzene only have one such channel is explained from the calculated potential-energy curves. These show that the lowering of point-group symmetry from C-2v to C-s along the main photodissociation reaction coordinate, which only occurs in o- and m-dibromobenzene, opens up a new predissociation channel. Dynamical quantum simulations based on the calculated potential-energy curves are used to estimate the coupling strength at the intersystem crossing point in bromobenzene. (C) 2004 American Institute of Physics.

D/H isotope-substitution effects on the Jahn-Teller (J-T) distortion of cation radicals of partially deuteriated benzenes, benzene-d5, benzene-1,2,4,5-d4, benzene-1,4-d2, and benzene-1,3,5-d3, were investigated by electron spin resonance (EPR) using frozen haloalkanes and porous silicas as matrices. Quantum-chemical calculations using the density functional theory (DFT) method were also performed. The way of distortion of the cation radicals of selectively deuteriated benzenes is unique relative to the deuteriation sites in all the matrices used. The ground state of the distorted cation is 2B 2g of D2h symmetry, regardless of the way of isotope labeling. The undeuteriated C-H bonds occupy the specific positions in the distorted form where the higher spin density appears, in agreement with the result of theoretical calculations. The role of the matrix to stabilize the distorted form is also discussed.

Results from ab initio Hariree-Fock and gradient-corrected density functional theory calculations of formic acid interactions with ZnO (1010) surfaces are reported. Surface relaxation is found to affect equilibrium geometries and adsorption energies significantly. Large variations in adsorption energy with coverage and ordering of the adsorbates are revealed and explained in terms of strong and highly anisotropic electrostatic adsorbate-adsorbate interactions. The results are compared to published experimental and theoretical results, and differences in suggested binding geometries from the different studies are discussed. Dynamic properties of the adsorption, surface mobility, and surface reactivity are inferred from key elements of the potential energy surface obtained from the quantum chemical computations and supported by ab initio molecular dynamics simulations. (C) 2002 Wiley Periodicals, Inc.

The electronic and molecular structures of an electrochemically reduced and oxidized triarylamine layer (((3-ethyl(p-N,N-dimethylamino)phenyl)amino)propyl-1-phosphonic acid) adsorbed on a nanocrystalline TiO2 film have been investigated. Photoelectron spe, Addresses: Westermark K, Univ Uppsala, Dept Phys, Box 530, S-75121 Uppsala, Sweden. Univ Uppsala, Dept Phys, S-75121 Uppsala, Sweden. Univ Uppsala, Dept Phys Chem, S-75121 Uppsala, Sweden. Univ Coll Gavle, S-80176 Gavle, Sweden.

Addresses: Univ Uppsala, Dept Quantum Chem, Box 518, S-75120 Uppsala, Sweden.

Deuterium isotope effects on the methyl group conformation and ESR spectra of selectively deuterated dimethyl ether radical cations are demonstrated by employing experimental matrix-isolation ESR techniques in combination with accurate ab initio and densi, Addresses: Shiotani M, Hiroshima Univ, Fac Engn, Dept Appl Chem, Higashihiroshima 739, Japan. Hiroshima Univ, Fac Engn, Dept Appl Chem, Higashihiroshima 739, Japan. Univ Uppsala, Dept Quantum Chem, S-75120 Uppsala, Sweden.

N 1s x-ray absorption spectra of bi-isonicotinic acid (2,2'-bipyridine-4,4(')-dicarboxylic acid) on rutile TiO2(110) have been studied experimentally and quantum chemically. Differences between multilayer and monolayer spectra are explained by the adsorba, Addresses: Persson P, Univ Uppsala, Dept Quantum Chem, Box 518, S-75120 Uppsala, Sweden. Univ Uppsala, Dept Quantum Chem, S-75120 Uppsala, Sweden. Univ Uppsala, Dept Phys, S-75121 Uppsala, Sweden. Univ Lund, MAX Lab, S-22100 Lund, Sweden. Paul Scherrer In

The interaction between dye and semiconductor is a central aspect of dye-sensitized solar cells. We have in this payer studied the binding of the common ligand bi-isonicotinic acid (4,4'-dicarboxy-2,2'-bipyridine) to TiO-2 anatase (101) surfaces by means, Addresses: Persson P, Univ Uppsala, Dept Quantum Chem, POB 518, S-75120 Uppsala, Sweden. Univ Uppsala, Dept Quantum Chem, S-75120 Uppsala, Sweden. Univ Coll Gavle, S-80006 Gavle, Sweden.

Results from quantum chemical INDO/S-CI calculations of the absorption properties of anatase TiO2 nanoparticles sensitized by catechol and benzoic acid are reported. Experimental observations that catechol causes a strong shift in the TiO2 absorption thre, Addresses: Persson P, Univ Uppsala, Dept Quantum Chem, Box 518, S-75120 Uppsala, Sweden. Univ Uppsala, Dept Quantum Chem, S-75120 Uppsala, Sweden. Univ Gavle, S-80006 Gavle, Sweden.

Bi-isonicotinic acid (2,2'-bipyridine- 4,4'-dicarboxylic acid) is the ligand of several organometallic dyes, used in photoelectrochemical applications. Therefore the atomic scale understanding of the bonding of this molecule to rutile TiO2(110) should giv, Patthey L, Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland. Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland. Univ Uppsala, Dept Phys, S-75121 Uppsala, Sweden. Univ Uppsala, Dept Phys Chem, S-75121 Uppsala, Swede

A series of Ru-polypyridine dyes has been studied with electron spectroscopy using AlK alpha and synchrotron radiation. Both pure complexes and complexes adsorbed on nanostructured TiO2 (anatase) surfaces have been examined and special emphasis was g, Rensmo H, Univ Uppsala, Dept Phys Chem, Box 532, S-75121 Uppsala, Sweden. Univ Uppsala, Dept Phys Chem, S-75121 Uppsala, Sweden. Univ Uppsala, Dept Phys, S-75121 Uppsala, Sweden. Solaronix Inc, CH-1170 Aubonne, Switzerland. Univ Uppsala, Dept Quantum Chem

Pyromellitic dianhydride-4,4'-oxydianiline (PMDA-ODA) polyimide films have been studied using high resolution x-ray photoelectron spectroscopy and model semi-empirical INDO/S-CI calculations. Experimental and theoretical C 1s, N 1s, and O 1s spectra are p, Addresses: Persson P, Toray Res Ctr Ltd, Sonoyama 3-3-7, Otsu, Shiga 520, Japan. Toray Res Ctr Ltd, Otsu, Shiga 520, Japan. Univ Uppsala, Dept Quantum Chem, S-75120 Uppsala, Sweden. IBM Corp, Thomas J Watson Res Ctr, Yorktown Heights, NY 10598 USA. Univ U

Pyromellitic dianhydride-4,4'-oxydianiline (PMDA-ODA) polyimide films have been studied using high resolution x-ray photoelectron spectroscopy and model semi-empirical INDO/S-CI calculations. Experimental and theoretical C 1s, N 1s, and O 1s spectra, Persson P, Toray Res Ctr Ltd, Sonoyama 3-3-7, Otsu, Shiga 520, Japan. Toray Res Ctr Ltd, Otsu, Shiga 520, Japan. Univ Uppsala, Dept Quantum Chem, S-75120 Uppsala, Sweden. IBM Corp, Thomas J Watson Res Ctr, Yorktown Heights, NY 10598 USA. Univ Uppsala, Dep

Lunell S, Univ Uppsala, Dept Quantum Chem, Box 518, S-75120 Uppsala, Sweden. Univ Uppsala, Dept Quantum Chem, S-75120 Uppsala, Sweden. Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden.

An ESR study was carried out to elucidate the static and dynamic Jahn-Teller structures of the radical cations of selectively deuteriated cyclohexanes in a cC(6)F(12) matrix, formed by exposure to ionizing radiation at low temperature. Based on the ESR sp, Shiotani M, Hiroshima Univ, Fac Engn, Dept Appl Chem, Higashihiroshima 739, Japan. Hiroshima Univ, Fac Engn, Dept Appl Chem, Higashihiroshima 739, Japan. Univ Uppsala, Dept Quantum Chem, S-75120 Uppsala, Sweden.