Inan Chen

Molecular Orbital Theory of Sulfur and Selenium Radicals

The electronic structures of various sulfur and selenium radicals were studied by semiempirical molecular orbital theory in the form of a parameter theory. The ESR data (g values) were used to determine the actual value of the parameter α, which is the coefficient of the s orbital in the bonding hybrid of the S(Se) atom in the radical. The physical significance of α so determined was studied by investigating some quantum chemical quantities such as valence state energies Ev and bond strengths B as functions of α. As a result, a criterion for the determination of the parameter value was deduced, namely, the selection of that value of α which maximizes B2 | Ev |.From theoretical considerations and experimental data in the literature, the relative signs of the principal values of the hyperfine‐structure tensor of selenium were determined, and the magnitudes of the isotropic and anisotropic components were evaluated.

ESR of α‐Copper Phthalocyanine. II. Powder Line Shape and MO Calculations

The ESR spectrum of polycrystalline α‐Cu phthalocyanine, reported by us previously, has been analyzed in detail by powder line shape and MO calculations. The superhyperfine (shf) tensors are shown to be essentially isotropic and hence the system can be described by an axial spin Hamiltonian. The low‐field spectrum consists of four well‐defined peaks from which the spin‐Hamiltonian parameters g‖ and A can be readily determined. The high‐field spectrum is a superposition of four sets of nine‐component lines over‐lapping to result in 15 almost equally spaced peaks. This fact suggests that the hyperfine (hf) constant B is about twice the shf constant aN. This relation has been used to estimate the values of g⊥, B, and aN. Only a slight adjustment of parameters was needed to synthesize a derivative line shape which fitted well to the experimental spectra. For one of the hf components (M = 32), the resonance field is not a monotonic function of θ, the angle between molecular axis and the magnetic field. The eff...

Electron Spin Resonance of the Organic Semiconductor, α‐Copper Phthalocyanine

Various concentrations of polycrystalline powders of α‐copper phthalocyanine diluted in nonparamagnetic α‐metal‐free phthalocyanine matrices have been studied by 8‐mm ESR at room temperature. The superhyperfine (SHF) spin Hamiltonian used in analyzing earlier results of ESR investigations on square‐bonded copper complexes has been reconsidered and a new SHF term is derived. The concentration‐dependent study has revealed enough separate features to enable observations to be interpreted by essentially considering the contributions of only two molecular orientations to the over‐all derivative line shape. Although single crystals of many organo‐metallic complexes, including α‐copper phthalocyanine, are not available, this study indicates that the relevant parameters of the spin Hamiltonian can in some cases be readily deduced from polycrystalline spectra.

g‐Value Calculations of Paramagnetic Centers in Amorphous Selenium

The g values of several possible models for paramagnetic centers in amorphous selenium are calculated by the method described in the preceding paper. The results of that paper show that the electron spin resonance lines of amorphous selenium reported to date cannot be attributed to free chain ends because of the disagreement in the calculated and observed g values. In this paper, we invoke interaction between the chain end and other atoms, including those in the same chain and in a neighboring chain, as well as impurities. The results show that the most probable source of the sharp line with g=2.0039±0.0006 is an oxygen impurity terminating the chain; the broad line with larger g values (2.3 to 2.8±0.01) can be interpreted as inhomogeneously broadened by pairs of interacting chain ends.

Band Structures of Metal‐Free Phthalocyanine in the β Phase

The excess electron and hole‐band structures of β‐metal‐free phthalocyanine are calculated with the tight‐binding approximation, using the Huckel molecular orbitals obtained previously by this author. The heteroatomic nature of the molecule is emphasized, and hence a new form of molecular potential, which reflects the nonuniform distribution of the pi electrons in the molecule, replaces the Goeppart–Mayer–Sklar potential used in previous band‐structure calculations of hydrocarbons. The interaction between the two electron bands formed from the two nearly degenerate lowest empty molecular orbitals has also been considered. The resulting band structures are qualitatively similar to those of anthracene, but with more pronounced anisotropy in the bandwidths. The velocity tensors 〈υiυj〉 and 〈υiυj / | υ |〉, where υ is the group velocity and υi, υj are its components, associated with a particular band are computed from the band structures for different values of vibronic overlaps. The applicability of the simple...

On the computation of Onsager quantum efficiency

A new method of computing the Onsager quantum efficiency of photogeneration is presented. This method is shown to be much faster than and as accurate as the series method used previously. Results applicable to a‐Si (dielectric constant=11.5) are given as an example.

Electronic Spectra and Molecular‐Orbital Calculations of Dioxazines

An iterative extended Huckel molecular‐orbital calculation for the π‐electron system has been carried out to interpret the electronic spectra of dioxazines. The absorption peaks in the visible have been identified as the transitions from the highest occupied orbital to the lowest empty one. It is found that the orbital energy difference contributes only about one‐third of the transition energy, the rest coming from the difference in the electronic repulsion energies of the ground and the excited states. The spectra in concentrated sulfuric acid solution can be interpreted as that of a diprotonated molecule. By assuming that the effective core charges of the nitrogen atoms to which the protons are attached are increased from 1 to about 1.5 proton charge, it is possible to account for the observed red shift of the band in the visible region. The calculated transition frequencies in the visible as well as in the uv are in good agreement with the observed ones.

Electrophoresis in liquid development of electrophotographic images

Liquid immersion development of electrostatic images involves the electrophoretic motion of charged toners and counter-ions in a spatially non-uniform and time-varying electric field originating from the imagewise charge on the photoreceptor. This paper summarizes the recent coordinated theoretical and experimental investigation of electrophoresis under a condition closely simulating the actual development process. The roles of chase density and mobility in the development process are elucidated by the theory of space-charge-limited transport. Their values are determined by a novel characterization technique, and are shown to be consistent with the prediction from the electrical double-layer model.