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Abstract: Origins of absorption shifts in polar liquids are considered for centrosymmetric chromophores devoid of dipole moments. The refractive index (n) dependent bathochromism shows that the excited state is always more polarizable than ground state. With increasing solvent dielectric constant (ɛ), mainly red shifts occur, but there are exceptions. Hypsochromism of n–π* transition in s-tetrazine is ascribed to a decrease of quadrupole moment in the excited state. In this case the upper level is pushed up in the reaction field of the ground-state quadrupole. Red shifts of intense bands in polyenes (11Bu or S2) and polyarenes (1Bb or β), reaching ∼−250cm−1 are assigned to local polarization in the reaction fields of chromophore bond dipoles. The hyperbolic-like ɛ-dependence of solvent shift, approximated to an empirical function (ɛ − n 2)/(ɛ − n 2 + c), is much steeper (with “stretching” factor c =3±0.5) in this case, as compared to that for the linear effect (for s-tetrazine, c =9). Polarization mechanism also causes less band broadening in polar environments. Contrary to a common view, the spectral shift is probing local reaction fields of chromophores, rather than random fields in the cavities accommodating the dye. Negligible polarization in solvent “cavity” fields is in accordance with earlier hole-burning study of matrix induced dipole moments in tetrapyrrolic pigments that depend surprisingly little on the polarity of polymeric hosts (R.B. Altmann, I. Renge, L. Kador, D. Haarer, J. Chem. Phys. 97 (1992) 5316 ). [Copyright &y& Elsevier]

Abstract: Most biological functions of carotenoids relate to strong visible absorption. In a quest to protein matrix effects on spectra, the shifts produced by solvent refractive index (n) and static dielectric permittivity (ɛ) were quantified for visible absorption maxima of β-carotene and a model compound with sharper bands, tetra-tert-butylnonaene ttbP9. The dispersive red shift that depends on optical dielectric constant n 2 is insensitive to polarity, in disagreement with previous work (H. Nagae, et al., J. Chem. Phys. 101 (1994) 6750). Small residual red shift in polar liquids obtained after subtraction of the dispersive component, obeys a static susceptibility function (ɛ − n 2)/(ɛ − n 2 +4). Because polyenes show little inhomogeneous band broadening in polar solvents, the shift was assigned mainly to quadratic Stark effect, rather than to a reaction field of quadrupolar origin, proposed earlier (N. Ghoneim, P. Suppan, Spectrochim. Acta A, 51 (1995) 1043). It is highly plausible that the chromophore is polarized in short-range “edge fields”, according to molecular dynamics/semiempirical simulations (F. Cichos, et al., J. Chem. Phys. 114 (2001) 6824), not in a uniform cavity field, as usually presumed. [Copyright &y& Elsevier]

A new formalism has been elaborated for calculations of hydrogen line profiles emitted by dense plasmas. The main equation of this formalism has a similar form to a set of close-coupled, time-dependent partial differential equations. Calculated line shapes are broadened, shifted and asymmetrical. The formalism yields both shifts and widths of a line calculated within the same theoretical approach. A new basis of the appropriate subspace of the Hilbert space has been built. This basis gives an accurate description of the quadratic Stark effect, and the interaction of the emitter with field gradients. The computer simulation has been used to determine the emitter perturbations by electrons and ions. Calculations were performed for the Balmer alpha line, because this line is a very helpful tool for a dense plasma diagnostic and there is a great interest in the shape of the line. Final results have been compared with experimental and theoretical findings of other authors. [Copyright &y& Elsevier]