Molecular Rydberg transitions: The lowest-energy Rydberg transitions of s-type in CH3X and CD3X,X = Cl,Br, and I

The absorption spectra associated with transitions to the lowest-energy s-type Rydberg states of CH₃X and CD₃X, X = Cl, Br, and I, have been measured and analyzed. The spectra of the bromides and iodides consist, individually, of four electronic origins of s-excitation type. The vibrational frequency of a given normal mode is more or less identical in all four excited states of any one molecule; and the excited state/ground state ratios of the frequencies of any given normal vibrational mode are essentially identical for all four molecules (i.e., for 16 states, four for each of two bromides and two iodides). The spectra of the chlorides are amenable to a number of different vibronic analyses, none of them unique; these analyses are discussed.     

Computer Resolution and Franck-Condon Analysis of the Electronic Absorption Spectrum of KMnO4 in Water

Abstract

The electronic absorptíon spectrum of KMnO₄ in water solution was analyzed. The spectral contour was resolved into component bands and then Franck-Condon approach was applied. In the investigated range of 13000–48000 cm^?1 a presence of three structureless and of two vibronic strong bands was stated. The change in the Mn-O equilibrium bond length was found to be 10.5pm for 2e·1t₁ transition (vibronic band about 18000cm^?1) and to be 16pm for the 2e·3t₂ transition (vibronic band about. 30000cm_?1). The appropriate wavenumber of the vibrational mode in these excited electronic states was found to be 735cm^?1 and about 780cm^?1, respectively. The ground electronic state wavenumber of the totally symmetric vibrational mode was fitted to be equal to 828cm^?1. Details of the proposed method of computer elaboration of electronic spectra with vibrational structure were discussed.

Electronic absorption spectra of some inorganic comppunds consist of a number of strongly overlapped bands due to their vibronic structure.^1–5 A detailed analysis of spectral contours of such compounds provides some useful information about their structure in both ground excited electronic states.

The electronic spectrum of permanganate ion is the typical example of vibronic spectra.¹ The main part of the past works based on the analysis of permanganate ion spectra in low temperatures and different polarizations. In such conditions the vibronic structure is rather good resolved and can be effectively studies.^1,3,6 Spectra of solutions as a rule are relatively poor resolved so their analysis has to be more sophisticated.

The main purpose of this work is a presentation of a new computer method for an effective study of vibronic spectra of solutions. This method has been applied to the electronic absorption spectrum of KMnO₄ in water. The method allowed us to fit the geometric parameters of spectral contour, to establish the origins and parameters of two progressions in the UV/VIS range as well as to calculate the changes in the Mn-0 equilibrium bond lengths and vibrational energy resulting from the electronic excitations of the soluted permanganate ion.     

T1uhg杨-泰乐系统：D5d势阱中的各向异性现象

杨-泰乐(Jahn-Teller缩写为JT)系统在其最低的绝热势能面上常常典型地含有一系列相互等同的势阱.在C60分子中，若一个电子占据该分子的三重简并的能量最低电子态，这一具有T1u对称性的电子态将会与具有hg对称性的五重简并振动态发生相互作用，形成所谓的T1uhg JT系统.当考虑电声的非线性相互作用时，该系统的势能面上将出现D5d对称性的势阱并伴随D3d对称性的势垒；反之亦然.本文在幺正平移变换的基础上，引入了标度变换，研究了该JT系统中D5d势阱中的各向异性现象：在电子空间中，非线性项的引入使得 关键词： C60 杨-泰乐效应 各向异性 电声耦合 标度变换     

Spectroscopic effects of conical intersections of molecular potential energy surfaces

A simple vibronic coupling model involving two electronic states and two vibrational modes is considered. The model is based on harmonic diabatic potentials and linear coupling of the diabatic electronic states. It is shown that the adiabatic electronic potential energy surfaces exhibit, in general, a conical intersection. The well known E × E and E × B Jahn-Teller problems are contained as special cases. Using numerical methods the optical absorption spectrum is calculated exactly. Extremely complex vibronic spectra are obtained when the conical intersection occurs within the Franck-Condon (FC) zone. The exact vibronic spectra are compared with spectra calculated in the adiabatic and FC approximation. The genuine spectroscopic effects of conical intersections are revealed by a comparison with the results of standard one-dimensional vibronic coupling calculations. The presence of a conical intersection limits the applicability of the adiabatic and FC approximations much more strongly than in the one-dimensional case. The upper adiabatic electronic state is strongly affected by non-adiabatic coupling even when the point of intersection lies outside the FC zone. The relevance of these results for the calculation of molecular electronic spectra is briefly discussed.     

Calculation and interpretation of vibronic absorption and fluorescence spectra of the first electronic nπ* transitions of pyridine and pyrimidine

We have calculated vibronic spectra of the first electronic nπ* transitions of pyridine and pyrimidine in the isolated state using the DFT method in the Franck-Condon approximation. Vibrational spectra for the ground and excited states have been calculated in the anharmonic approximation, which allowed us to refine the assignment of normal vibrations of pyridine and pyrimidine. We have done a complete interpretation of the vibrational structure of the absorption and fluorescence spectra of pyridine and pyrimidine. It has been shown that Fermi resonances between fundamental and combination vibrations and overtones 12 and 16b + 4, 6a and 2 × 16b affect the formation of the vibrational structure of electronic spectra of pyrimidine. Good agreement between calculated and experimental spectra confirms the correctness of the models of the two molecules in their ground and excited states, which makes it possible to use the models in further investigations of various properties of these molecules in electronically excited states, e.g., tautomerism of pyrimidine bases of nucleic acids.     

Rotational transitions in degenerate vibrational states of C3v symmetric top molecules,with application to CH3C15N

General algebraic expressions for the vibration-rotation energy levels and the associated rotational transitions of C_3v symmetric top molecules are developed. These expressions are presented in a convenient form for analysing the spectra of a molecule with any degree of excitation of a degenerate vibrational mode and have been applied to the spectrum of CH₃C¹⁵N.     

High-Resolution, Rotationally Resolved Electronic Spectroscopy of the MgNC Radical

High-resolution, rotationally resolved, laser-induced fluorescence (LIF) spectra for the origin band, as well as several transitions involving vibrationally excited levels of the ?2Pi <-- &Xtilde2Sigma+ electronic transition of the MgNC radical, have been recorded using the output of a pulse-amplified Ti:Sapphire ring laser. The MgNC radical was generated in a supersonic free jet expansion by simultaneous laser ablation of a magnesium rod and photolysis of acetonitrile (CH3CN). Rotational analysis yielded molecular constants for both the ground and excited states of the studied vibronic transitions. The molecular constants for the vibrationless state of the &Xtilde state are in excellent agreement with previous microwave studies of MgNC. Since the ? electronic state of MgNC is a linear 2Pi state, the bending vibronic level structure is subject to both Renner-Teller and spin-orbit coupling. Suggested vibronic assignments of the observed transitions, made considering both these interactions and with the aid of the rotational analysis, are discussed. Copyright 1999 Academic Press.     

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.     

Electron resonance studies of the renner effect

The gas phase electron resonance spectra of NCO in its ground ²Π_3/2 vibronic state and in two excited vibronic states are described. Theoretical analysis of the spectra yields effective g values for the three states. In additon the ¹⁴N magnetic hyperfine and electric quadrupole coupling constants and the electric dipole moment are determined. The theory of the Renner coupling of electronic and vibrational motion is extended, and shown to account for anomalous contributions to the g values. The theory also shows that these contributions are closely related to the Renner coupling constant.     

Spectroscopic ramifications due to cancellation effects in special degenerate electronic states

Various cancellation effects occurring in special kinds of spatially degenerate electronic states are discussed. The ramifications of the cancellation effects on the IR and Raman vibrational spectra, microwave rotational spectra, and electronic spectra are elucidated.     

Calculation and interpretation of the absorption and fluorescence spectra of indole in the isolated state and aqueous solution

We have calculated the vibronic absorption and fluorescence spectra of the first (¹ L _b ) and second (¹ L _a ) electronic transitions of indole in the isolated state and aqueous solution. The vibrational structure of the absorption and fluorescence spectra has been interpreted. The influence of the aqueous solution on the vibronic spectra has been shown.     

T1u×hg Jahn-Teller系统：D3d势阱中的频率分解与能级分裂

在C60分子中，未被填充的最低电子态具有T1u对称性，因此，对中性的C60而言，不论是通过分子内部激发，或是外部掺杂，都易被一个电子占据而形成Jahn-Teller（JT）活跃电子态.此态与五重简并的hg声子态耦合，构成所谓的T1u-hg -JT系统.在这一JT系统中，当只考虑电声的线性耦合时，其绝热势能面是一个槽形.但在实际的系统中，二阶电声耦合是存在的，理论研究表明，原来的势槽将被这二阶非线性耦合弯曲成D3d或D5d对称性的势阱.声子振动态在阱中将显示各向异性效应，使得声子沿不同的方向有不同的振动频率，进而影响势阱中的能级分布、势阱间的重叠积分，以及整个系统的隧道能级分裂等.对D3d势阱中各向异性效应进行了研究，利用幺正平移、?pik Pryce和标度变换等方法计算了系统势阱中的能级，以及阱中的振动频率，研究了势阱中的能级间隔以及微绕修正能量的变化，并由此导出了这些物理量在仅有线性耦合的势槽中变化的情形. 关键词： C60 Jahn-Teller效应 各向异性 电声耦合     

Vibronic structure of the 3s Rydberg state of the 2-methylallyl radical

Resonance-enhanced multiphoton ionization combined with electronic ground state depletion spectroscopy of jet-cooled 2-methylallyl (C₄H₇) radicals provides vibronic spectra of the 3s and 3p Rydberg states. Analysis of the vibronic structure following one-photon and two-photon excitation of rovibronically cold 2-methylallyl radicals and its isotopologues C₄H₄D₃ and C₄D₇ reveals transitions to more than 30 vibrational levels in the 3s Rydberg state that are identified and reassigned on the basis of predictions from ab initio calculations and results from pulsed-field-ionization zero-kinetic-energy photoelectron spectra obtained with resonant multiphoton excitation via selected intermediate states. Depletion spectroscopy reveals transitions to short-lived 3p Rydberg states that have a large oscillator strength.     

A theoretical analysis on the vibronic spectra with mass analyzed threshold ionization spectroscopy

We have theoretically studied the absorption vibronic spectra with the resonance two-photon (R2P) and non-resonance two-photon (NR2P) mass analyzed threshold ionization (MATI) spectroscopy. The theory uses the inverse Born-Oppenheimer approximation (IBOA) to establish a proper basis set. To analyze the MATI vibronic spectra, we have calculated the Franck-Condon factors involved in the vibronic transitions. Several experimental spectra are analyzed using this theory with emphasis on the importance of the resonance intermediate states. The long vibrational progression in a MATI spectrum can be partly attributed to the result of including the anharmonic correction in the calculated Franck-Condon factors. The experimentally observed isotope effect is also analyzed.     

Selection rules for rovibronic transitions in symmetric top molecules

A simple diagrammatic rule is presented for determining the rotational selection rules governing transitions between any pair of vibronic states in electric dipole spectra of symmetric top molecules. The rule is useful in cases where degenerate vibronic levels with first-order Coriolis splittings occur, because it gives immediately the selection rule for the (+l) and (-l) components in any degenerate state. The rule is also helpful in determining the symmetry species and the effective zeta constants in overtone and combination levels involving degenerate vibrations. Particular attention is devoted to the conventions concerning the signs of zeta constants.     

Vibronic fluorescence and fluorescence excitation spectra of diphenyl oxazolyl benzene and its oxadiazol analogue

The fine-structure fluorescence and fluorescence excitation spectra of conjugated chain compounds—1,4-di(5-phenyl-2-oxazolyl) benzene and its oxadiazol analogue—are obtained at 4.2 K in an n-octane matrix using the Shpolskii method. The spectra are modeled by representing the band of each of the vibronic transitions as the sum of a zero-phonon line and a phonon wing with certain parameters (half-widths, Debye-Waller factors). The spectra calculated in this fashion coincide with the experimental spectra. This makes it possible to determine the relative intensities of vibronic transitions and refine the frequencies of the normal vibrations in the S ₀ and S*₁ states. The parameters of the Franck-Condon and Herzberg-Teller interactions in the molecules considered are determined. The influence of the replacement of one of the CH groups in the heterocycles with a N atom on the parameters determining the formation of vibronic spectra is considered.     

Electronic Raman scattering and infrared absorption by arsenic acceptors in ZnTe

We have measured electronic Raman scattering spectra and infrared absorption spectra of arsenic doped ZnTe. Electronic transitions from the ground state to the excited states in the arsenic acceptor and also vibronic transitions accompanying 1 LO phonon have been observed in both spectra. Experimentally determined acceptor levels are compared with the theoretical calculation.     

Two-photon vibronic spectroscopy of allene at 7.0–10.5 eV: experiment and theory

2?+?1 resonance-enhanced multiphoton ionization (REMPI) spectra of allene at 7.0–10.5?eV have been observed. The excited vibronic symmetry has been determined from polarization-ratio measurements. Based on the vibronic energies and peak intensities calculated using ab initio MO and time-dependent density functional theory, the very congested REMPI spectra have been assigned as due to π*?←?π, 3p?←?π, 4s?←?π, 4p?←?π, and 4d?←?π transitions. Vibrational progressions related to the CH₂ twisting (ν₄ ～770?cm^?1) have been observed for several excited electronic states. Calculated Franck–Condon factors also confirm that CH₂ twisting is the most active mode in the vibronic spectra of allene. In this study, theoretical calculations of two-photon intensities and polarization ratios have been made through the ab initio computed one-photon transition dipole moments to various electronic states as intermediates. As a starting point to interpret the complicated vibronic spectrum of allene, the theoretical approach, without vibronic couplings, has been applied to predict the peak positions, spectral intensities, and polarization ratios of Rydberg states, and qualitatively shows a considerable agreement with experimental observations.     

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.     

Vibrational transitions in Rydberg matter clusters from stimulated Raman and Rabi‐flopping phase delay in the infrared

Recently, rotational spectra of giant Rydberg matter (RM) clusters were studied in the radio frequency range (Mol. Phys. 105 (2007) 933–939), giving high‐precision bond distances in the nanometer range. However, the theoretical and experimental problem of vibrational motion or, rather, coupled electronic‐vibrational motion in the RM clusters is still unsolved; but it is expected that broad phonon bands will exist. Spectroscopic signatures from space make it likely that RM is a common form of matter in the Universe, and phonon bands in this spectroscopic range have not been taken into account so far. Spectroscopic results are now reported on transitions in the range 0.01–20 cm⁻¹, using primarily infrared (IR) lasers to probe the RM in a tunable open cavity with a Fabry–Perot interferometer to aid in the identification of the shifts. Stimulated Raman scattering from electronic transitions and Rabi‐flopping from electronic states in the clusters are observed. The broad stimulated Raman peaks are assigned to one and two consecutive vibrational (electronic‐vibrational) transitions. Theoretical values predicted for vibrations (phonon maxima) and electronic processes are in reasonable agreement with the experimental results. Improved calculations are needed to verify the assignments of the vibrational phonon distributions. Copyright © 2008 John Wiley & Sons, Ltd.