Configuration vibronic mixing for a neutral vacancy in silicon and diamond

Configuration vibronic mixing is considered for a fully symmetric Jahn-Teller electronic term with orientation-degenerate terms (due to the distortion direction) including a correlation correction in a single-open-shell approximation. The approach is nonempirical and involves only linear vibronic coupling. The adiabatic potential is a multiwell one, because the different configurations involved in the exact Jahn-Teller term have different vibronic coupling with a lattice distortion. The stabilization energy, the frequencies of local lattice vibrations, the vibronic coupling parameter, and the energy barriers to migration and to distortion-axis reorientation are estimated for a neutral vacancy in silicon and diamond with allowance made for configuration vibronic coupling. The estimates agree with the results obtained by different experimental and theoretical methods for a wide range of properties associated with the Jahn-Teller effect.     

Charge transfer excitons: dynamic theory of vibronic spectra

The vibronic spectra of charge transfer excitons (CTE) in a molecular one-component or alternatingly ordered two-component chain are treated in the framework of a dynamic approach (neglecting thermal excitations of the intramolecular vibrations). The model introduces two mechanisms of coupling between CTEs and vibrational quanta: (1) shift of the equilibrium positions of the nuclei in the ionized donor or acceptor; (2) change of the vibrational frequency in the ionized molecule. This model allows to generalize the simple CTE Hamiltonian and the vibronic Hamiltonian of Frenkel excitons. The linear optical susceptibility is calculated in the vibronic region (one CTE and one vibrational quantum). The double splitting of vibronics of CTEs was analyzed: (1) the splitting connected with the location of the intramolecular vibration on the donors or on the acceptors; (2) the splitting connected with the symmetry of the vibronic spectra (in the degenerate case). The general structure of the vibronic spectra of CTEs is established. It contains structureless absorption lines, which correspond to two-particle bands (the phonon is excited on a neutral molecule neighboring the donor or the acceptor) and Lorentz-type lines of one-particle states, which correspond to the bound propagation of the CTE and the phonon.     

On the theory of vibronic superradiance

The Dicke superradiance on vibronic transitions of impurity crystals is considered. It is shown that parameters of the superradiance (duration and intensity of the superradiance pulse and delay times) on each vibronic transition depend on the strength of coupling of electronic states with the intramolecular impurity vibration (responsible for the vibronic structure of the optical spectrum in the form of vibrational replicas of the pure electronic line) and on the crystal temperature through the Debye-Waller factor of the lattice vibrations. Theoretical estimates of the ratios of the time delays, as well as of the superradiance pulse intensities for different vibronic transitions well agree with the results of experimental observations of two-color superradiance in the polar dielectric KCl:O ₂ ^? . In addition, the theory describes qualitatively correctly the critical temperature dependence of the superradiance effect.     

Influence of spin-orbit coupling on vibronic spectra of metalocomplexes porphin: Manifestation of out-of-plane vibrations

In fine-structure phosphorescence spectra of metallocomplexes of porphin with ions of the Pd(II) and Pt(II) and their meso-deuterated derivatives additional lines have been detected which have no analogs in fluorescence and resonance Raman spectra of metalloporphyrins and in phosphorescence spectra of metallocomplexes of porphin with light ions of the Mg(II) and Zn(II). For Zn-porphin, quantum-chemical calculations of frequencies and forms of in-plane and out-of-plane vibrations have been performed. Based on experimental data and calculation results it has been found, that in vibronic phosphorescence spectra of metallocomplexes of porphin, out-of-plane gerade modes of the E _g symmetry (D _4h symmetry group) are manifested. The activity of out-of-plane vibrations increases with enhancing spin-orbital coupling upon changing to heavier chelated metal ions. Vibronic transitions with participation of out-of-plane gerade E _g vibrations manifest in the T ₁ → S ₀ transition through the vibronic intensity borrowing from the triplet-triplet ³ E _u -³ E _g transition.     

Evidence for a vibronic spectrum in the photoluminescence of thoria

The photoluminescence spectrum obtained at 77 K for undoped and doped thoria samples produced by thorium nitrate thermolysis reveals the presence of a fine structure, which is interpreted as a vibronic spectrum. The two vibrational frequencies which can be deduced from this spectrum agree with the values found by IR and Raman techniques. The possible origin of the vibronic spectrum is discussed.     

Experimental determination and interpretation of the fluorescence and fluorescence excitation spectra of chrysene cooled in a supersonic jet

The fluorescence and fluorescence excitation spectra of jet-cooled chrysene are measured. The frequencies of in-plane vibrations in the ground and first excited singlet electronic states, as well as the relative intensities of transitions between them, are calculated with the MO/M8ST method. Based on these data, experimental spectra are interpreted. In the fluorescence excitation spectrum, the position of the line of the 0–0 transition (28 195 ± 1 cm^?1), which is the most intense, is determined. In the experimental fluorescence excitation spectrum, 21 lines correspond to fundamental vibrations (altogether, 37 lines are attributed). This supports our assignment and is consistent with the group-theoretical analysis of vibronic interactions. Upon excitation at the frequency of the 0–0 transition, 10 lines corresponding to the excitation of fundamental vibrations are detected, and all 17 lines observed are attributed. In the fluorescence excitation spectrum, the standard deviation between the calculated and measured frequencies of attributed fundamental vibrations is 19 cm^?1, while that in the fluorescence spectrum is 15 cm^?1.     

Resonance Raman profile with consideration for quadratic vibronic coupling

A relation is found between the first-order Raman profile and the absorption spectrum of a scattering centre with regard to the quadratic vibronic coupling in a zero-temperature case. Two non-degenerate electronic states of the centre are considered, the adiabatic and Condon approximations are used, and the vibrations of the centre are assumed to be harmonic.     

Fluorescence and fluorescence excitation spectra of jet-cooled carbazole

The fluorescence excitation spectra of jet-cooled carbazole molecules at vibrational temperatures of 55 and 80 K and the fluorescence spectrum of these molecules excited by radiation at the frequency of a pure electronic transition are measured. As the vibrational temperature increases, the excitation spectra exhibit a series of lines of the same symmetry, which are caused by the interaction of the active vibration with a subensemble of optically inactive vibrations. The final symmetry of the totally and nontotally symmetric vibrations is determined from the shape of the rotational contours of the lines of vibronic transitions. The values of a decrease in the frequency of the nontotally symmetric vibrations in the first excited electronic state S ₁ due to their interaction with the electronic state S ₂ are calculated to be up to 100 cm^?1. The frequencies of the pure electronic transitions in the absorption and fluorescence spectra coincide with each other and are equal to 30809 cm^?1, the frequencies of vibrations in the ground state S ₀ exceeding the frequencies of the corresponding vibrations in the excited state S ₁. The degree of polarization of the integral fluorescence is determined for a series of vibronic transitions of the a ₁ and b ₂ final symmetry that are observed in the fluorescence excitation spectra, and the contribution of the intensity with the borrowed polarization θ_⊥ to the integral fluorescence is calculated. It is found that the intensity θ_⊥ is higher for the transitions of the b ₂ symmetry and can reach ≈50%.     

Anharmonicity of lattice vibrations induced by charged nickel impurities in II–VI semiconductors

The lattice vibrations induced by nickel impurities with a negative charge relative to the lattice in ZnSe: Ni, ZnO: Ni, ZnS: Ni, and CdS: Ni semiconductors are investigated using very sensitive field-induced vibronic spectroscopy. This technique is based on the interaction of lattice vibrations with impurity excitons and the effect of an ac electric field on these excitons. The phonon replicas of the zero-phonon line (ZPL) of impurity excitons (including intense peaks of combination replicas up to the eighth order) in the experimental spectra of the system under investigation are observed for the first time. These spectra make it possible to analyze the interaction between different vibrations. The experimental results are interpreted in terms of model calculations of the vibrations in a lattice with a charged impurity center and vibrations in a monoatomic chain with a strong anharmonicity. It is demonstrated that charged impurity centers initiate new lattice vibrations, namely, extrinsic anharmonic modes with a considerable third-or fourth-order anharmonicity.     

Model of the lattice dynamics and study of the vibronic structure of intracenter transitions in ZnO:Ni+2 crystals

This paper presents a calculation of the defect vibrations induced in a ZnO:Ni crystal by the Ni⁺² impurity. The computations are done by a recursive method in the shell model. Based on the model calculations, the vibronic structure in the absorption spectra of the intracenter d-d transitions in the ZnO:Ni crystal is interpreted. Fiz. Tverd. Tela (St. Petersburg) 40, 2213–2216 (December 1998)     

Isotopic effect in the vibronic spectra of europium compounds

The effect of the kinematic factor on vibronic spectra of europium compounds and Eu³⁺-doped lanthanide compounds was examined experimentally. It was demonstrated that isotopic or quasi-isotopic substitution of the ions of the crystal lattice gives rise not only to the changes of the vibration frequencies but also to alteration of the value of electron-phonon interaction. The latter displays in changing the relative integral intensity of vibronic sidebands of electronic transitions of Eu³⁺ ion. Eu³⁺ vibronic spectra of a number of pairs of natural and isotopically or quasi-isotopically substituted compounds: nitrates, halides, formates, acetates, oxalates, β-diketonates, etc., were studied. In most cases the substitution of deuterium for hydrogen was applied. Decrease of the electron-phonon interaction with the increase of the isotopic mass depends on different structural characteristics. It was found that a factor of decreasing the relative intensity of the vibronic sideband of electronic transition of Eu³⁺ ion lies within the range ∼1.2 and ∼7 for pairs of compounds under investigation. The largest change of the intensity of vibronic sidebands was observed in a pair of formates Eu(HCOO)₃ and Eu(DCOO)₃ having the tridentate-bridging coordination of the formate anions and a three-dimensional frame structure. One should take into consideration both decreasing the vibration frequencies and diminishing the value of electron-phonon interaction at introduction of heavy isotope or quasi-isotope in the crystal lattice of lanthanide compounds to reduce the multiphonon quenching of luminescence.     

光致发光光谱研究金刚石光学中心的振动结构

金刚石中不同的缺陷中心具有不同的振动结构. 间隙原子相关中心在离开零声子线165 meV之外存在强且尖锐的局部振动模; 空位相关中心具有很强的振动耦合, 在其零声子线之后出现很强且宽的声子边带, 而在165 meV之外却观察不到局部振动模, 且对于仅涉及一个空位的缺陷来说, 其振动都与一个能量约为42 meV的声子或一个能量约为67 meV的声子或两声子有关.     

Vibronic Structures of the Ground and Excited Singlet Electronic States of Dimethylnaphthalenes Cooled in a Supersonic Jet

Abstract

Fluorescence excitation and dispersed fluorescence spectra of jet-cooled naphthalene and 2,6-, 2,7-dimethylnaphthalenes have been measured. The frequencies of optical active vibrations in the ground and first excited singlet states have been determined. The new technique for calculation of planar vibration frequencies of polycyclic benzenoid hydrocarbons in the excited electronic states has been developed. The vibration frequencies in the ground and first excited singlet states of these molecules were calculated using the developed technique and the Ohno's model. The interpretation of vibronic spectral lines based on the comparison of the calculated and experimental data was made. The calculation rms errors for the vibration frequencies in the ground electronic states of the investigated molecules do not exceed 20 cm^?1 and are approximately 1.5 times higher for excited states without additional adjustment of parameters for individual molecules.     

The nature of the vibronic coupling in a metalloporphyrin and its Raman scattering

It has been shown that a Raman line of a nontotally symmetric vibration (b_1g, b_2g, or a_2g) of a metalloporphyrin (D_4h) can be caused, not only by a vibronic coupling between the first ($\text{A}\text{?}$) and second ($\text{B}\text{?}$) excited electronic states but also by a vibronic coupling within one of the electronic states (let us call the former the QS mechanism and the latter the QQ and/or SS mechanism). A simple formulation has been made for each of those different mechanisms, so that a numerical calculation can be made of the excitation profile of a Raman scattering for a given set of coupling constants and damping factors. Next, the result of an examination is given of the excitation profile of the Raman scatterings of some of the b_1g, b_2g, and a_2g vibrations of nickel octaethylporphyrin and nickel octaethyltetrachloroporphryin. Most of the Raman lines of these nontotally symmetric vibrations show a resonance effect only in the Q-band ($\text{A}\text{?}\text{←}\text{X}\text{?}$) region but not in the Soret-band ($\text{B}\text{?}\text{←}\text{X}\text{?}$) region. On the basis of this fact, it has been suggested that those Raman lines are caused mainly by the QQ mechanism rather than the QS mechanism. The observed vibrational structure of an excitation profile also seems to support this suggestion.     

Ab initio investigation of the vibronic structure of the C2H spectrum

A purely ab initio study of the vibronic structure of the X ²Σ⁺, A ²Π system of C₂H is presented. An approach is developed for a simultaneous treatment of three electronic states coupled via the bending and C-C stretching vibrations. On the basis of the results of the present calculations, it is possible to reliably interpret previous experimental findings.     

The influence of geometry on the vibronic spectra of quantum aggregates

A study is presented of the localisation of excitonic states on extended molecular aggregates composed of identical monomers arising, not from disorder due to statistical energy shifts of the monomers, induced by environmental interactions (Anderson localisation), but rather simply due to changes in the orientation and geometrical arrangement of the transition dipoles. It is shown further that such small changes nevertheless can have a drastic effect on the shape of the vibronic spectrum of the aggregate. The vibronic spectra are calculated using the ‘coherent exciton scattering’ (CES) approximation whose derivation we generalise to be applicable to aggregates of arbitrary size and geometry.     

A renormalization scheme for calculating the spectrum of a vibronic system occurring in molecules or impurities in insulators

An iteration scheme which makes use of a numerical renormalization group approach is used to calculate the spectrum of vibronic levels. This spectrum resulted from dynamic effects occurring in certain molecules or impurities in insulators.The Hamiltonian of these systems is expressed in the matrix form, using products of suitable electron-phonon states as a basis. In applying this method to multimode electron-phonon systems, phonon modes are coupled in a chain-like fashion. Then a finite chain calculation in terms of Hubbard X-operators is explored by setting up the vibronic Hamiltonian.Calculations are based on Lanczos algorithm, in which only the nearest neighbor matrix elements along the chain need to be taken into account. The iterative scheme is then applied to a two-level electronic system coupled to phonons. A single-particle Green's function corresponding to a two-level system is applied to calculate the spectral density of states, which, coupled to single mode is carried out. The strength of lines in density of states is affected by the coupling constant as well as the temperature dependence of some measurable quantities.     

Theorie vibronischer Spektren in Ionenkristallen

The electronic bands of some foreign ions in a crystal exhibit one or a few intermixed sequences of equidistant lines (vibronic spectra.) Examples are the divalent rare-earth ions in alkali-halide and alkaline-earth-halide crystals. It is shown that such sequences of lines are only possible if a) the disturbed lattice dynamics gives rise to localized or quasi-localized modes and b) the electronic functions of the defect ion (properly symmetrized in the static crystal field) do not overlap the nearest lattice ions. To calculate the single lines of a vibronic band a refined method of moments is developed. Its parameters (oscillator displacement and frequency change) follow from the dynamics of the disturbed lattice. The lattice vibrations are calculated by means of modern scattering theory. To describe the scattering resonance the advantageous concept of metastable (quasi-localized) vibrations is introduced. Then the projection of the cartesian coupling functions of first and second order onto the disturbed lattice eigenvectors can be determined. Their matrix elements <n|U _x |n> and <n|U _xx |n> define the change of the equilibrium positions and frequencies during the transition. Further on general symmetry-selection rules are derived for the electron-lattice coupling. Finally the important case of a pure electrostatic coupling is discussed in more detail. It is evident that the study of vibronic spectra gives important information about the dynamics of the disturbed lattice and the electron-lattice coupling. Especially they constitute a method to investigate localized and quasi-localized modes, even if their dipole moment is too small for direct optical excitation, or if their frequency lies in the absorbing region of the crystal.     

在群论框架下电子三重态与声子耦合的理论研究

本文基于绝热近似和群论导出了电声耦合系统的哈密顿量的一般形式,讨论了电声耦合系统中的电子算符和活跃的声子模式. 应用幺正平移变换和能量最小化方法,进一步计算了正四面体群下T*(e+t₂)杨-泰勒系统中的激发态能量,从对称性的角度分析了T₁电子态的能级分裂以及晶格体系的对称性破缺,得出了对称性的破缺方式和电声耦合系统密切相关的结论. 结果表明:通过群论与对称性分析完全可以定性地解释由于电声耦合所造成的简并电子 关键词： 电声耦合 杨-泰勒畸变 活跃的杨-泰勒声子模式 电声耦合哈密顿量     

Mesoscopic superpositions of vibronic collective states of N trapped ions

We propose a scalable procedure to generate superpositions of motional coherent states and also entangled vibronic states in N trapped ions. Beyond their fundamental importance, these states may be of interest for quantum information processing and may be used in experimental studies on decoherence.