Electronic Structure and Spectra

We think of the ionic solids as made up of closed-shell ions, so that to a first approximation, the electronic structure is like that of the inert-gas solids. Two important differences arise, however, from the transfer of protons to make ions first, the electronic states on different ions are not the same and, second, the spacing is sufficiently reduced that there are important effects from the matrix elements between states on adjacent ions. It will be best to begin with the simplest description, as we have in other systems, and introduce complications as we go one reason for this is that many properties are understandable without the full complexity of the true electronic structure. 

Let us again take KCl as a prototypic system and center our discussion on the alkali halides. It appears that most of the concepts necessary for understanding the entire range of ionic solids arise already in these simple systems. 

We begin with atomic argon, shown on the extreme left in the energy-level diagram in Fig. 14-1. The 3.s and 3p levels are fully occupied and the excited state of lowest energy is the 4.v level. Above that is the ionization energy of argon. 

Formation of the energy-band structure of KCl. We start with argon atoms, and then put them in a simple-cubic crystal structure. Protons arc then transferred between neighboring nuclei to form potassium and chlorine ions. 

Finally, we transfer protons between adjacent nuclei, converting the atom which gives up the proton to a chlorine ion, and converting the atom which receives it to a potassium ion. This splits each of the bands into a chlorine band and a potassium band. The cxcilon level is also split the exciton deriving from the chlorine is lifted into the conduction band, as shown. 

A number of LCAO calculations have been reported (49, 186, 265, 289), but perhaps the most detailed study has been that of Basu (14), who used a simple Hiickel treatment. 

The relative energies of the lowest 18 molecular orbitals are illustrated in Fig. 14. These are only approximate since configurational interaction has been ignored. The electron densities and mobile bond orders are shown in Fig. 15, assuming different coulombic integrals for the carbon and nitro- 

In Table IV are listed all the available electronic absorption data for the phthalocyanines with the exception of some of the earlier work (330, 337). Table V lists the spectra of some phthalocyanines in the solid state, and Fig. 16 illustrates the spectra of metal-free phthalocyanine and of the zinc derivative. 

All normal oxidation state phthalocyanines are characterized by an intense band near 28,000 cm-1 (Soret band), and another intense band near 14,000-15,000 cm-1. Metal-free phthalocyanine differs in having an intense doublet near 14,000-15,000 cm-1. The intensities are of the order of 106 (dipole strength 1-2 A2) (138). Films as thin as 30 A are reported, by virtue of their color, to be visible to the naked eye (165). Because of the 14,000- 

Complex Solvent Visible and ultraviolet absorption spectra1,c,i Reference 

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Anisimov V I, Aryasetiawan F and Liechtenstein A I 1997 First-principles calculations of the electronic structure and spectra of strongly correlated systems The LDA+U method J. Phys. Condens Matters 767... 

McWeeny, R., and Peacock, T. E., Proc. Phys. Soc. A70, 41, The electronic structure and spectra of some nitrogen hetero-benzenes."... 

Mataga, N., Nishimoto, K. Electronic structure and spectra of some nitrogen heterocycles. 

Sherman, D.M. (1985) Electronic structures of Ee " coordination sites in iron oxides application to spectra, bonding and magnetism. Phys. Chem. Min. 12 161-175 Sherman, D.M. (1987). Molecular orbital (SCF-Xa-SW) theory of metal-metal charge transfer processes in minerals I. Application to the Fe vpe charge transfer and electron delocalization in mixed-valenced iron oxides and si-licates.Phys Chem Min 70 1262-1269 Sherman, D.M. (1990) Crystal chemistry, electronic structure and spectra of Fe sites in clay minerals. Applications to photochemistry and electron transport. In Coyne, L.M. McKeever, S.W.S. Blake, D.F. (eds.) Spectroscopic characterization of minerals and their surfaces. A.C.S. Symposium Series 415, 284-309... 

Kraus, M. (1994). Electronic structure and spectra of the peroxynitrite anion. Chem. Phys. Lett. 222, 513-516. 

Electronic Structures and Spectra of Aromatic Hydrocarbons and N-Heterocyclic Compounds N. Mataga, Kagaku toKogyo (Tokyo), 1965,18, 1289-1296. 

VII. Tautomerism, Electronic Structures, and Spectra of Rare Pyrimidine Bases of the Nucleic Acids. 312... 

When Lenore McEwen was appointed in 1959, she became the first woman named as a theoretical chemist on the faculty of a department of chemistry of a Canadian university. She maintained her interest in the electronic structures and spectra of nitrogen-oxygen compounds for several years after her arrival in Saskatoon, although most of her papers resulted from her postdoctoral research in Sandorfy s group.69... 

K. L. McEwen,]. Chem. Phys., 34, 547 (1961). Electronic Structures and Spectra of Some Nitrogen-Oxygen Compounds. 

Though ab initio calculations continue to improve and we expect them to take a laiger role in the future, we do not expect them to totally supersede parametrized models. Parametrized models provide valuable insights into electronic structure and spectra. They also give an efficient way of dealing with a variety of interesting optical properties in a large number of materials. 

Further evaluations [164,165] have demonstrated the applicability of the fitted system of parameters for calculations of the electronic structure and spectra of numerous complexes of divalent cations using merely the CNDO parametrization for the /-system. In [140,169] the EHCF method is also extended for calculations of the ligands by the INDO, MINDO/3, and SINDO/1 parametrizations. In all calculations the experimental multiplicity (spin) and spatial symmetry of the corresponding ground stales were reproduced correctly. The summit of this approach has been reached in [170] by calculations on the i.s-[Fe(NCS btbipyjo] complex. Its molecular geometry is known both for the HS and LS isomers of the said compound. The calculation... 

Malaga, N., and K. Nishimolo Electronic structure and spectra of nitrogen heterocycles. Z. Physik. Chem. 13, 140 (1957). 

Tanaka, M., and S. Nagahura Electronic structures and spectra of adenine and thymine. Theoret. Chim. Acta (Berlin) 6, 320 (1966). 

Harris DL, Loew GH (1996) Identification of putative peroxide intermediates of peroxidases by electronic structure and spectra calculations. J Am Chem Soc 118 10588-10594... 

M. L. Kirk, B. L. McNaughton, and M. E. Helton, Prog. Inorg. Chem., 52 (2004) This chapter deals with the electronic structure and spectra of dithiolene complexes. 

The electronic structures and spectra of the M02 FSBOs are problematic,102103 while for tungsten there is no doubt that strong W=W triple bonds exist. 

Electronic Structure and Spectra of Light Alkali Diatomic Molecules and Their Molecular Cations... 

Halgren, T. A. Lipscomb, W. N. J. Chem. Phys. 1973, 58, 1569. See Konowalow, D. D. Rosenkrantz, M. E. "The Electronic Structure and Spectra of Light Alkali Diatomic Molecules and their Molecular Spectra" ACS S nnp. Series, 1981. 

The first theoretical studies on AI2O3 were of electronic structure and spectra. Photoelectron studies on AI2O3 (Balzarotti and Bianconi, 1976 Gignac et a ., 1985) show a two-peak O 2p valence band with a peak separation of 4-4.7 eV and an overall width of about 8.5 eV (Fig. 4.7). Cluster calculations using the MS-SCF-Aa method (Tossell, 1975a), and the semi-empirical molecular-orbital EHMO (Ciraci and Batra, 1983) and CNDO... 

Experimentally, the direction of a transition moment in a molecule can he evaluated by four methods (i) polarized spectra of single crystals, (ii) fluorescence or phosphorescence polarization, (iii) spectra of molecules embedded in stretched Aims, and (iv) spectra of molecules oriented by external fields. Only relative directions of the transition moment can be determined by means of the last three methods, whereas the polarized spectra of single crystals give the absolute direction of the moments if the crystal structure is known. The first method has been applied to the study of the electronic structure and spectra of several pyrimidine bases of nucleic... 

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