Anomalous light absorption in molecular crystals

The method of successive approximations is used to obtain a solution for an infinite chain of nonlinear coupled equations for the Fourier transform of the retarded two-time Green’s function in a system in which the electron vibrational interactions of the lattice photons and of the intramolecular photons are included in the terms of the Hamiltonian that are diagonal in the electron operators. A unique subsequence, which provides a finite contribution to the integral intensity of the absorption spectrum, is extracted from the infinite series and summed. The resulting formulas are used to classify the excited states of a crystal and interpret the cases of anomalous light absorption, when the absorption intensity becomes inversely proportional to the Franck-Condon overlap integral. Zh. éksp. Teor. Fiz. 112, 1021–1040 (September 1997)     

The polarized reflection and absorption spectra of perylene crystals in monomeric and dimeric forms

The electronic absorption spectra of perylene crystals in the α- and β-forms were measured by the normal incidence reflection method in the spectral region from 20 000 to 60 000 cm^?1. From the absorption spectrum polarized perpendicular to [1$\text{1}$0] axis of the α-form crystal, the bands around 24 000 cm^?1 were determined to be polarized along the long molecular axis. Two strong bands with different polarizations were observed around 50 000 cm^?1 for each of the α- and β-perylene crystals and were assigned to the transitions to the ¹B_2u and ¹B_3u states. The observed polarized absorption spectra as a whole were consistent with the theoretical results by Hummel and Ruedenberg and the reflection method was found to be suitable to the polarized absorption measurement of strong bands of crystals. The observed factor-group splittings were compared with the theoretical values, the oriented gas model being found to be applicable to the β-form crystal.     

Symmetry-relations and dynamics of molecular crystals in the long wave limit

Symmetry relations for macroscopic constants are derived. Especially it is shown that the Voigt-symmetry holds for the indices of the elastic constants. This has been doubted several times for lattices of particles with additional degrees of freedom. In the second part a simple model for Br₂- and J₂-lattices is discussed. The intermolecular forces are assumed to be van-der-Waals-forces. The influence of the internal degrees of freedom on lattice dynamics is calculated especially for the elastic constants. Further the limiting frequencies forq?0 are given and compared with experimental values.     

Dynamical diffraction theory for wave packet propagation in deformed crystals

We develop a theory for the trajectory of an x ray in the presence of a crystal deformation. A set of equations of motion for an x-ray wave packet including the dynamical diffraction is derived, taking into account the Berry phase as a correction to geometrical optics. The trajectory of the wave packet has a shift of the center position due to a crystal deformation. Remarkably, in the vicinity of the Bragg condition, the shift is enhanced by a factor omega/deltaomega (omega: frequency of an x ray, deltaomega: gap frequency induced by the Bragg reflection). Comparison with the conventional dynamical diffraction theory is also made.     

Numerical analysis of the reflection and absorption of electromagnetic wave in nonuniform magnetized plasma slab

In this paper, a model for calculating the reflection and absorption powers of electromagnetic wave (EM wave) in nonuniform magnetized plasma slab is given out based on layer propagation theory. The effects of various plasma parameters and different values of magnetic field intensity on the reflected and absorbed powers are discussed. The results illustrate that the thickness of plasma seldom affects the reflection of radar wave, but it can broaden or reduce the absorption width. Meanwhile, the background magnetic field intensity has an influence upon the results, and it could change the resonance spectrum of magnetized plasma. We also find out that, with appropriate plasma density, collision frequency and magnetic field intensity, more than 90% of radar wave power can be absorbed and the resonant absorption band is about 2 GHz.     

Theory of line shape of optical absorption and emission spectra in molecular crystals

We solve the equations of the coupled coherent and incoherent motion of excitons in molecular crystals and determine the optical line shapes and positions including Davydov splitting.     

On the theory of anomalous absorption of an ordinary wave

We obtain and analyze numerically exact formulas for anomalous absorption of a probing ordinary wave due to its transformation into plasma waves under vertical sounding of an ionospheric plasma layer with given spectrum of irregularities. The nature of possible approximations and their validity limits are analyzed. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 8, pp. 826–836, August 1999.     

On the apparent absence of triplet-triplet absorption in pure organic molecular crystals

The triplet-triplet absorption spectra of naphthalene-h ₈ in a 3-methylpentane glass at 77 K and naphthalene-h ₈ in a naphthalene-d ₈ crystal at 4·2 K are reported. A broad continuum absorption unique to the mixed crystal spectrum is believed to be due to a guest-induced transition into the host conduction band. Absence of the absorption in pure crystals of naphthalene at temperatures ranging from 1·8 K to 300 K is also discussed.     

Transfer matrix theory for the optical absorption spectrum of mixed crystals

We study the density of states and optical absorption spectrum of linear mixed crystals in the one- dimensional alloy transfer matrix approximation. Local modes, which are present in the single impurity limit, develop into collective modes by merging into a band as the impurity concentration increases. The composition dependence of local and collective like optical absorption peaks is discussed, and we show that qualitatively different behaviours are obtained for single band and split bands type density of states.     

On the theory of temperature shift of the absorption curve in non-polar crystals

On the assumption that valence or conduction electrons move in a periodic potential field produced by ions oscillating around their equilibrium positions an expression is derived for the dependence of the temperature shift of the absorption curve for non-polar substances of diamond structure or with a ZnS type of crystal lattice. By a method analogous to the procedure in investigating the temperature dependence of the intensity of Laue-Bragg maxima for the diffraction of X-rays it is shown that for lower temperatures this dependence is at first quadratic, later linear and at high temperatures an exponential function of the temperature. It is proved that in contrast to previous theories the qualitative character of this dependence is in agreement with experience. It is shown that for diamond, silicon and germanium the numerical values are also of the same order as the measured values.     

On the Born-Oppenheimer approximation of wave operators in molecular scattering theory

In this paper we study the diatomic molecular scattering by reducing the number of particles through Born-Oppenheimer approximation. Under a non-trapping assumption on the effective potential of the molecular Hamiltonian we use semiclassical resolvent estimates to show that non-adiabatic corrections to the adiabatic (or Born-Oppenheimer) wave operators are small. Furthermore we study the classical limit of the adiabatic wave operators by computing its action on quantum observables microlocalized by use of coherent states.     

The role of Frenkel excitons in low-energy-electron diffraction theory for molecular crystals

In this paper a low-energy-electron diffraction theory for molecular crystals is established. The possibility of creating Frenkel excitons by the incident low-energy electrons is taken into account. The whole formalism is based on a set of diagram rules, which facilitates the evaluation of the differential scattering cross section. The influence of the bulk and surface excitons on the LEED intensities will be discussed in a series of subsequent papers.     

声波的吸收与反射

测量声波幅度随传播距离变化的实验曲线,用波动学的观点分析实验数据,考虑到吸收和反射等耗散因素,计算出空气的吸收系数和换能器的反射系数.     

Optical absorption spectra of I3 - molecular ions in KI crystals and aqueous solutions

A semiempirical molecular orbital method including spin-orbit interaction is used to study optical absorption spectra of I₃ ^- molecular ions in (KI + I₂) aqueous solutions and in KI crystals coloured additively or electrolytically. The splitting of two strong absorption bands observed for these specimens is considered to be due to the spin-orbit interaction in the iodine atoms. The values of the spin-orbit coupling constants for I₃ ^- in aqueous solutions and coloured KI crystals are estimated to be 0·56 and about 0·47 eV, respectively. The oscillator strengths of the two strong bands for these specimens is also discussed.