Interpretation of electronic spectra by configuration analysis: Absorption spectra of monosubstituted naphthalenes with an electron-accepting group

The electronic absorption spectra of four monosubstituted naphthalenes with an electron-accepting group, 1- and 2-naphthonitriles and 1- and 2-naphthaldehydes, have been investigated by means of configuration analysis with particular attention to the dependence of spectra on the position of substitution. The results of molecular orbital calculations based on the Pariser-Parr-Pople method were analyzed in terms of locally excited states and charge-transfer configurations. The characteristic changes in location of the L_b, L_a, and B_b bands caused by the substitution at 1- or 2-position are adequately explained by the analysis for monosubstituted naphthalenes with an electron-accepting group as well as for those with an electron-donating group. The results of the present configuration analysis for naphthalene derivatives with an electron-accepting group are compared with the results for those with an electron-donating group.     

Interpretation of electronic spectra by configuration analysis MO theoretical interpretation of the spectral changes caused by substitution in naphthalene

The spectral changes caused by the introduction of a substituent into naphthalene are mainly dependent on the position of the introduced substituent but are almost independent of the electron-donating or the electron-accepting nature of the substituent. An attempt was made to analyze this using the MO theoretical interpretation of the spectral changes in substituted naphthalenes based on the method of configuration analysis. It was found empirically that the magnitudes of the spectral shifts are determined primarily by the extent of charge-transfer contributions. From the analysis of the contribution of charge-transfer configurations, the spectral behavior characteristic of the substituted naphthalenes is satisfactorily interpreted by the pairing properties of naphthalene molecular orbitals.     

Polarization measurement and configuration analysis of the triplet-triplet absorption spectra of substituted naphthalenes

The polarization of triplet-triplet absorption spectra for 1- and 2-methoxynaphthalene, 1,5-, 1,8-, 2,7-, and 2,3-naphthalenediols, and 1,4-dimethoxynaphthalene was measured by the photoselection method. Calculations of the triplet states of these molecules were made by the Pariser-Parr-Pople method, and the resulting wavefunctions were subjected to the configuration analysis. The T-T absorption spectra of the β-substituted naphthalenes are relatively simple and closely resemble that of naphthalene. In the α-substituted naphthalenes, the T-T absorption spectra are not only remarkably different from that of naphthalene but also different from one another. Comparison of experimental and theoretical results leads to reasonable assignments of the individual absorption bands involving some modification of previous assignments. The apparent complexity of T-T absorption spectra of the α-substituted naphthalenes can be interpreted in relation to the enhanced and transitions of naphthalene.     

Vibrational spectra of monosubstituted acetylenes

The frequencies and envelopes (modes) of the normal vibrations of the molecules CH₃CCH, FCCH, BrCCH, and ICCH have been calculated and their force constants determined.     

Infrared absorption spectra of some monosubstituted benz-2,1,3-thiadiazoles

The IR spectra in the 500–1900 and 2800–3200 cm^–1 regions were recorded for six compounds: 4- and 5-methyl-, 4- and 5-chloro-, and 4- and 5-bromobenz-2,1,3-thiadiazoles. An assignment is given for some of the bands.Translated from Izvestiya VUZ. Fizika, Vol. 11, No. 8, pp. 18–22, August, 1968.     

Interpretation of the electronic spectra of phthalocyanines with transition metals from quantum-chemical calculations by the density functional method

Using the time-dependent formalism of the density functional theory (time-dependent density functional theory (TDDFT)), the energies and intensities of the electronic transitions of some metal phthalocyanines of transition metals and of their anionic forms with different electron localization are studied quantum chemically. It is shown that, in all the cases studied, calculations using the B3LYP functional with even a comparatively narrow basis set (6–31G) are quite consistent with the previous calculations of the same objects by the ZINDO/S-CI semiempirical method taking into account double excitations. For a number of particular examples, it is shown that a lack of consideration of doubly excited configurations in the calculation of excited states by the TDDFT method can be compensated by the contribution from single excitations, which proves to be more significant due to the presence of the correlation component of the exchange-correlation functional.     

Surface electronic spectra detected by atomic desorption

Using continuously tunable laser excitation of KI we measure the desorption yield of hyperthermal iodine atoms as a function of photon energy. Based on a theoretical model of desorption we demonstrate that these spectra display a signature of a surface exciton and constitute a new sensitive method of surface electronic spectroscopy detected by atomic desorption. Our results not only demonstrate that creation of surface excitons can be a much more general phenomenon than was previously thought, based on measurements made using established spectroscopic techniques, but extend the classes of material amenable to surface spectroscopic interrogation.     

Interpretation of the electronic spectra of Fe and Co porphyrins based on quantum-chemical calculations by the density functional method

Using the time-dependent formalism of the density functional theory (time-dependent density functional theory (TDDFT)), the energies and intensities of the electronic transitions of some Fe and Co porphyrins and their anionic forms with different electron localization are studied quantum chemically. It is shown that, in the majority of the considered cases, the calculations performed with the B3LYP functional with a comparatively narrow basis set (6-31G) are quite consistent with previous calculations of these objects by the ZINDO/S-CI semiempirical method taking into account double excitations. Furthermore, the level of agreement of the B3LYP calculations with experiment is the same as that obtained with the ZINDO/S-CI method.     

Band shape analysis of electronic spectra of polar dye solutions

A semiclassical theory of electronic spectra of polar dye solutions is presented and analytical expressions of the spectra are given. A quasi-molecular approach is applied and the quasi-molecule model of the spectra previously published is reanalyzed. It is assumed that a large-amplitude motion plays a key role in the broadening of the spectra of polar dye solutions. An energy-level diagram of a quasi-molecule, considered as a dye molecule with its nearest neighborhood, is presented. In addition, the energy of reorientation in going from a Franck-Condon to an equilibrated state is determined. The orientation energy is equal to that part of the excitation energy given by the difference of the excited Franck-Condon state of a quasi-molecule from that of its equilibrated excited state. It is shown that after excitation, not only is excess vibrational, but also part of the electrostatic interaction energy is transferred to the surroundings. This energy may be obtained directly from absorption and fluorescence spectra of polar dye solutions. Experimental verification is performed on several coumarin solutions. The mean value for the reorientation energy in this case is found to be 645 cm_–1.     

Absorption spectra of actinide compounds

From the energy levels of the gaseous ions Ac⁺⁺, Th⁺⁺⁺, and Th⁺⁺, it can safely be extrapolated that the ground electron configuration of all actinide ions with ionic charges at least + 3 contains only 5f-electrons outside the emanation shells. This is further supported by the 5fⁿ → 5f^n-16d transitions observed in Pa(IV), U(III), Np(III) (though their wave numbers are too high to be measured in U(IV) and Np(IV)). The configuration f² has a very characteristic distribution of energy levels between ³H₄ and ³P₂ with ¹S₀ as much higher, isolated level. The absorption spectra of U(IV) complexes and of PuF₆ suggest interelectronic repulsion parameters ～60 per cent of the values in the corresponding lanthanides, while the Landé factors are about twice as large. This would also explain the recent measurements of Cm(III) complexes, compared to Gd(III). The larger average radius of the 5f-shell causes larger perturbation effects from the ligands than in the lanthanides. The J-values will therefore be distributed between several adjacent, observed energy levels without making the general treatment of the fⁿ-configurations impossible. The variation with oxidation numbers in isoelectronic series are discussed, e.g. U(III) and Np(IV); Pu(III) and AmF₄; and Am(III) and CmF₄. Band positions are predicted in Bk(III) and BkF₄. Finally, the chemical properties of the actinide elements are discussed, and it is emphasized that no necessary connections exist between the presence of f-electrons and constant trivalency.     

Absorption spectra of germanium nanocrystals

Absorption spectra of hydrogenated germanium nanocrystals are calculated in real space using ab initio pseudopotentials constructed within the local density approximation. Nanocrystals with over 800 atoms are considered. We find the calculated spectra are essentially bulk-like for systems with ∼250 atoms or more. The energy positions for the E₁ and E₂ reflectivity peaks are blue-shifted with respect to their bulk values owing to quantum confinement. Comparisons with available experimental data reveal good agreement for the energies of the E₁ peak, whereas the energy position of the E₂ peak is underestimated by a constant shift, which is independent of the nanocrystal size. This shift is consistent with local density calculations for bulk germanium.     

Some electronic spectra of dibenzofuran

The low-energy electronic states of dibenzofuran have been investigated by absorption and emission spectroscopy. The absolute intensity of absorption parallel to the a and b axes of a single crystal at room temperature has been measured from 32 000 to 42 000 cm^?1, and qualitative information about the strength of the c-axis absorption was obtained from a study of finely-ground dibenzofuran compressed in KBr discs. The symmetries of three transitions were determined and tentative assignments of two others were made. The absorption bands in the spectrum of the crystal held at 4.2 K remained broad, an effect attributed to exciton-phonon interaction. Spectra of dibenzofuran in a polycrystalline n-heptane matrix at 4.2 K were sharp and vibrational analyses of fluorescence and phosphorescence are given in terms of the known ground state fundamentals.