2b 2g Research Articles

Electron paramagnetic resonance and optical absorption spectra of Cu 2+ ions in alkali barium chlorophosphate glasses

The results of measurement of electron paramagnetic resonance and optical absorption spectra at room temperature of alkali barium chlorophosphate glasses (BaCl 2–M 2O–P 2O 5) doped with 1 mol% CuO are presented for various alkali compositions (M=Li, Na, K, Li–Na, Na–K and K–Li). The results indicate that the mixed alkalies do not produce alterations of the glass network. The ground state of Cu 2+ is the d 〈 x 2− y 2〉 orbital and the site symmetry that exists around the Cu 2+ ions is octahedral with a tetragonal elongation. The theoretical optical basicity of the glasses have been evaluated and the changes in optical basicity are independent of changes in spin-Hamiltonian parameters of the Cu 2+. The optical absorption spectra of Cu 2+ ions for all the glass samples was single asymmetric band which corresponds to a 2B 1g → 2B 2g transition. By correlating the spectral data, the molecular orbital coefficients α 2 and β 1 2 for Cu 2+ have been evaluated and results indicate that there is covalency for the in-plane σ-bonding and that the in-plane π-bonding is significantly ionic in nature.

ENDOR and EPR studies of benzene radical cations in halocarbon matrices: the static Jahn–Teller distortion of the monomer and geometry of the dimer cation

ENDOR investigations of the benzene radical cation in a CFCl 3 matrix at 30 K gave evidence for a static Jahn–Teller distortion with the unpaired electron density predominantly in the 2b 2g orbital. In this distortion the equivalence of the six protons is lost, with the major spin densities on H 1 and H 4. From ENDOR measurements the isotropic and dipolar couplings were accurately measured ( a iso=−25.31 MHz (H 1 and H 4) and a iso=−5.43 MHz (H 2, H 3, H 5 and H 6)) which agree with those reported earlier from EPR measurements and theoretical calculations. (C 6H 6) 2 +., formed by warming in CFCl 3 at 140 K and initially present in CF 3CCl 3, was characterised with ENDOR and assigned to a π-electron complex. The intermolecular distance was estimated from the measured dipolar hyperfine coupling to be in the range 2–3 Å.

Theoretical study on the ionized states of ethylene by the SAC-CI (general- R) method

The SAC (symmetry adapted cluster)/SAC-CI (configuration interaction) general- R method is successfully applied to the photoelectron spectrum of ethylene. The theoretical spectrum satisfactorily reproduces the outer- and inner-valence regions of the spectrum. The exponential generation (EG) algorithm followed by perturbation selection (PS) is shown to be useful in the generation of small and yet effective higher-excitation operators for the SAC-CI general- R method. The peak at 23.7 eV is assigned to the `twinning' ionized states, the 2 2A g and 3 2A g states, and the peak at 27.4 eV is attributed to the 6 2A g and 7 2A g states. In the energy region around 31 eV, some ionized states are suggested to locate with small intensities. The 1 2B 2g state obtains its intensity by the initial state configuration interaction.

Energy-dependent vibrational excitation by electron impact in thin films of amorphous benzene

The vibrational excitation of 10-layer films of amorphous solid benzene has been measured by electron-energy-loss spectroscopy at various incident energies between 1.2 and 14.7 eV. The high resolution of the spectra in connection with the energy dependence leads to a comprising assignment of the observed bands. The 2B 2g shape resonance is located between 3.2 and 4.2 eV which is about 1 eV lower than in gaseous benzene. The 2E 2u resonance is shifted to energies lower than 1.2 eV and is therefore not detected. The e 2u vibration, the excitation of which was previously discussed only through the 2E 2u resonance channel, is observed at all impact energies.

Electron paramagnetic resonance and optical absorption studies on vanadyl doped alkali tetraborate glasses

Electron paramagnetic resonance (EPR) and optical absorption studies have been made for VO(II) ions in alkali tetraborate glasses. The EPR spectrum shows eight hyperfine lines characteristic of VO(II) ions. The spin-Hamiltonian parameters, Fermi contact interaction parameter K, dipolar hyperfine coupling parameter P have been evaluated from the spectra. The anisotropy energy of the VO(II) ions have also been calculated. The values of the spin-Hamiltonian parameters confirm that V 4+ ions are present in the glasses as VO(II) molecular ions in an octahedral site with a tetragonal compression. The theoretical values of optical basicity (^ th) of glasses have also been evaluated. The optical absorption spectra of VO(II) ions in these glasses show two bands corresponding to the transitions 2B 2g → 2B 1g and 2B 2g → 2E g in the order of decreasing energy respectively. By correlating the electron paramagnetic resonance data and optical data, the molecular orbital coefficients have been evaluated.

Resonance Raman study of Franck-Condon effects in the C 10H 8+ radical. Ab initio MCSCF calculations for the low-energy 2B 2g and 2B 3g symmetry states

Resonance Raman spectra in the region corresponding to the 2 A u ( D o ) → 1 2 B 3 g ( D 2) electronic excitation of the naphthalene cation (C 10H 8 +) are studied in terms of a model based on Franck-Condon (FC) effects. This simple model correctly accounts for the RRS spectra and yields FC parameters which correspond to those obtained from ab initio MCSCF computations. Computed FC activities of nine totally symmetric modes in the 2B 3g(D 2) and 2B 2g(D 4) states of the C 10H 8 + radical are discussed and compared to experiment and earlier theoretical based studies on the ROHF/3-21G approach.

Electron paramagnetic resonance and optical absorption studies of Cu(II) ions in cadmium malate pentahydrate single crystals

The X-band electron paramagnetic resonance (EPR) studies on a single crystal of Cu(II) ion doped in cadmium malate pentahydrate have been studied over an extended temperature range of 120–390 K. The detailed analysis of EPR spectra reveal that the Cu(II) ion enters the Cd(II) site in the host lattice. From the observed EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The optical absorption spectrum exhibits a broad band and a shoulder which are assigned to the transitions 2 B 1g → 2B 2g and 2 B 1g → 2E g respectively. The ground state wavefunction of Cu(II) at room temperature is evaluated.

Synthesis and activity of aryl benzyl methyl sulfonium salts as cationic initiators: Effect of substituent on aryl group

AbstractBenzyl o‐, m‐, and p‐substituted phenyl methyl sulfonium salts (2b–2g) were synthesized and their activities as cationic initiators were evaluated in the bulk polymerization of phenyl glycidyl ether (PGE). Especially, their activities were estimated with respect to the effect of substituents on the aryl groups. In the polymerizations of PGE with a series of benzyl p‐substituted phenyl methyl sulfonium salts, the order of their activities was found to be 2c (CH3OCOO) > 2b (CH3COO) > 2d (CH3O) ∼ 2a (HO). In particular, 2c was the most active initiator of all, capable of initiating the polymerization of PGE even at room temperature. In the polymerizations with 2a, 2e (m‐Cl), 2f (o‐CH3), and 2g (m‐CH3), the activity of 2e was the highest of all while those of 2a, 2f, and 2g were almost the same. These results strongly suggested that the electron‐withdrawing group placed on the aryl group undoubtedly enhanced the activity of the sulfonium salts as the cationic initiators.

Photoexcitations of the Si −4 anion. Theoretical study

Some stable and metastable (autodetaching) excited states of the Si − 4 anions are characterized with the use of the first-order correlation orbital method and the coupled-cluster method. There are three doublet states of the anion, X 2B 2g, 2B 1g and 2B 1u, which lie below the electron ejection threshold. All other states have total energy higher than the energy of the neutral cluster.

Ab initio MRD-CI study of GaAs -, GaAs 2(±), Ga 2As 2(±) and As 4 clusters

Using pseudopotentials and double zeta basis sets with s, p diffuse functions and two sets of d functions, MRD-CI calculations were performed on As 2 (±), As 4 (+), GaAs −, GaAs 2 (±) and Ga 2As 2 (±). This study complements previous theoretical investigations on Ga (±) to Ga 4 (±) and GaAs (+). For As 4 tetrahedral symmetry was assumed, and Re of X 1A 1 determined as 4.73 a 0. Vertical ionization potentials to several states of As 4 + were calculated. For GaAs 2, GaAs 2 + and GaAs 2 −, ground and one low-lying state were geometry-optimized, both in C 2v (Ga-As-As), and linear symmetry (GaAsAs, C ∞h and AsGaAs, D ∞h). The lowest state of GaAs 2 is 2B 2 in C 2v. For Ga 2As 2, the lowest state and low-lying excited states were optimized in various geometries. The most stable state has rhombic structure ( 1A g in D 2h), but T-form and other forms (C 2v, C ∞v, D ∞h) are only 1–2 eV less stable. In D 2h symmetry, several low-lying excited states of Ga 2As 2 were studied. The ground states of Ga 2As 2 + and Ga 2As 2 − were found to be 2B 2u, and 2B 2g, respectively. Trends in ionization potentials (IP), electron affinities (EA), atomization energies and fragmentation energies for the molecules Ga x As y and the pure compounds Ga n and As n up to 4 atoms, were studied. Ga x As y clusters, with x + y even, have higher IP's than odd-numbered clusters. An experimentally observed alternation of EA, whereby an odd number of atoms have higher EA than their even neighbors, is confirmed. The mixed compounds Ga x As y have atomization energies between those of Ga n and As n ( x + y = n), usually closer to those of Ga n . Fragmentation of Ga x As y occurs such that As-As bonds are retained, and if possible, also Ga-As bonds, since the dissociation energy of As 2 is higher than that of GaAs, which in turn is higher than that of Ga 2. Calculated fragmentation energies agree qualitatively with experimental observations about the composition of 3-atomic and 4-atomic clusters Ga x As y .

Manifestation of the Jahn-Teller active vibrations in the vibronic spectra of tetracoordinate Cu 2+, Ni 2+ and Zn 2+ chlorides

An attempt is made to track the changes in the vibrational modes that are Jahn-Teller active of some pseudotetrahedral MCl 4 2− ions. The infrared and Raman spectra of powder (Et 4N) 2MCl 4, M=Ni, Cu, Zn and of Cu- and Ni-doped (Et 4N) 2ZnCl 4 were recorded both at room temperature and at 77, 100 and 170 K. The room temperature spectra show that for NiCl 4 2− and CuCl 4 2− if present the Jahn-Teller distortions are dynamically averaged and the transitions can be accounted for as intrasheet vibronic transitions. The low-temperature spectra however show splittings that are indicative of a low symmetry field thus suggestingthat at 77 K the NiCl 4 2− and CuCl 4 2− are vibronically stabilized in a static C 2v field. The doped compound spectra reveal that the Zn matrix effect overrides the static Jahn-Teller distortions present in the free ion spectra. In the CuCl 4 2− spectrum a band at 2700 cm −1 with side bands + v(a 1), − v(t 2 s) was detected and it was assigned to the 2B 2g→ 2B 1g transition arising from the split 2T 2 term in D 2h site symmetry.

Electronic spectra of p-difluorobenzene cation by mass-selected ion dip spectroscopy in a supersonic jet

The 2B 3u(π, π)←D 0( 2B 2g) transition of p-difluorobenzene ( p-DFB) cations prepared by two-color resonance-enhanced multiphoton ionization (REMPI) has been observed by mass-selected ion dip spectroscopy utilizing dissociation. All the spectra due to the transitions from different vibrational levels in D 0 showed vibrationally resolved structures. It was found from their vibrational analysis that there exists a strong vibronic coupling between the 2B 3u(π, π) state and the nearby (σ, π) state, and the former is the lowest excited state. The nonemissive property of p-DFB cation forms an exception to the generally accepted criterion that all fluorobenzene cations having the lowest excited (π, π) state are emissive.

Syntheses and characterization on nickel group complexes of two new 1,2-dithiolenes containing the tetrathioethylene unit

The synthesis of the 1,2-dithiolene dianion, (bis(methylthio)-1,2-dithiolate: MTDT 2−) along with bis complexes with Ni(III). Pd(III) and Pt(III) are reported. In addition, the syntheses of the Pt(III) and Pd(III) complexes of a second 1,2-dithiolene (5,6-dihydro-1,4-dithiin-2,3-dithiolate: DDDT 2−) which also contains the tetrathioethylene unit are reported. The reduced, M(II), complexes can also be isolated in an air free environment. Cyclic voltammetric data for each complex were typical of ‘dithiolenes’. These data allowed the authors to determine a stability order for 1,2-dithiolene complexes for both M(II) and M(III) oxidation states. ESR data were obtained for all new M(III) complexes. A rhombic symmetry was evident from the presence of three well defined g values in frozen glass spectra. We were able to utilize the Maki approach to determine the ground state electronic configurations for the Ni(III) and Pd(III) complexes. Those results support a d yz HOMO for both Ni(III)L 2 2− and Pd(III)L 2 −. Comparison of the Pt(III) data with that for other Pt(III) dithiolenes suggest a 2B 2g ground state.

Theoretical assignments of the electronic states of the π-radical cation of ethylene

Ab intio SCF and CI calculations on the ground and lower excited states of the radical cation are reported which employ a gaussian basis of double zeta quality augmented by polarisation functions. The best values obtained for the vertical excitation energies are 2B 3g(3.6 eV), 2A g (4.5 eV), 2B 2u (6.1 eV) and 2B 2g(6.2 eV). Cl calculations support the ab intio SCF prediction of a planar ground state geometry for the ion.

A kinetic study of the hydrolysis of acetonitrile co-ordinated to platinum, yielding platinblau

Molecular orbital and crystal field calculations suggest that for iron phthalocyanine the 3A 2gground state corresponds to the electronic configuration e 2 g b 2 2g a 2 1g, while for cobalt phthalocyanine the ground state is 2A 1g-e 4 gb 2 2ga 1 1g. The MO results imply a differential covalency within the set of orbitals d xy, d xz, d yz and d z 2 and it is necessary to invoke this concept in the crystal field calculations in order to reproduce the ground state of iron phthalocyanine and the low energy electronic transitions of both molecules. The calculations indicate that, contrary to a recent suggestion, the medium intensity bands in the near infra-red region of both these complexes are due to d → d electronic transitions. The bands are assigned 2 A 1g → 2E g and 2B 2g for cobalt phthalocyanine and 3 A 2g → either both 3 E g and 3B 2g for iron phthalocyanine.

Effects of symmetry-restricted covalence on the electronic spectra of tetragonal copper(II)-ammine compounds

The relative energies of the 2B 2g and 2E g states in tetragonal copper(II)-ammine complexes are discussed in terms of a model which takes account of symmetry-restricted covalence. The two-electron terms which arise in expressions for the dd transition energies are calculated in the INDO approximation, using eigenvectors obtained from experimental ESR data and a simple approximation based on perturbation theory. These lead to the prediction that for square coplanar Cu(NH 3) 2+ 4 the 2B 2g state should lie higher in energy than 2E g if the b 2g and e g orbitals are accidentally degenerate, as indicated by the angular overlap model. However, it is shown that the approach of axial ligands having π-donor orbitals leads to the ordering 2E g > 2B 2g, notwithstanding the destabilization of the e g orbitals by π-interaction with the axial ligands. These results are in accordance with the available experimental data.

Copper(II) complexes of N,N′-dibenzylethylenediamine

The following complexes of N,N′-dibenzylethylenediamine (DBEn) of copper(II) have been prepared: CuDBEn 2Cl 2,H 2O; CuDBEn 2X 2 (X = Cl, Br, I, and NO 3); CuDBEn 2SO 4,2H 2O; CuDBEn 2(ClO 4) 2,H 2O and CuDBEnX 2 (X = Cl, Br). They have normal magnetic moments, almost invariant with temperature. From the low temperature reflectance spectra of the mono(amine) complexes, evidence for the three 2B 1g → 2A 1g; 2B 1g → 2B 2g; and 2B 1g → 2E g transitions expected for a tetragonally-distorted complex has been obtained. The coordination of anions in the tetragonal positions of the bis(amine) complexes is established from their reflectance, solution and infrared spectra, and molar conductances except for the perchlorate, which is considered to have a highly distorted, virtually planar structure. The compound CuDBEn 2Br 2 can also be obtained in a form which from its reflectance spectrum may be five-coordinate.

The effect of coordination with a metal on reactivity of π-bonded organic ligands I. redox properties of some rhodium- and iridium-quinone complexes

The coordination with a metal versus the reactivity of π-bonded organic ligands has been studied for π-C 5H 5-Rh and -Ir complexes with quinones by polarographic methods. It was observed that in an acetonitrile solution of the coordinated quinones the reversible reduction waves of the above complexes shifted to the negative potentials with respect to the non-coordinated ligands. The analogy of the polarographic data for both coordinated and non-coordinated quinones allows the conclusion that the electronic density changes in the quinone part of the complex during the reduction on the mercury-dropping electrode. The coordination with -RhC 5H 5 is likely to increase the energy of the 2b 2g orbital of the quinone by over 0.9 eV and over 1.1 eV in the case of -IrC 5H 5.