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.     

Fine-structure spectroscopy of 2-methylnaphthalene cooled in a supersonic jet

The fluorescence and fluorescence excitation spectra of 2-methylnaphthalene molecules cooled in a supersonic jet are measured. The frequencies of vibrations in the S ₀ and S ₁ states, as well as the relative intensities of electronic-vibrational transitions in the fluorescence and fluorescence excitation spectra, are calculated with the semiempirical MO/M8ST method. The intensities are calculated in the Franck-Condon approximation taking into account the mixing of all the 38 totally symmetric normal vibrations. Based on the calculations, most observed spectral lines are assigned. It is shown that the calculation accuracy of the method is high enough for it to be used to interpret the spectra of molecules of aromatic compounds such as substituted naphthalenes. It is found that the main contribution to the fluorescence spectrum is made by four optically active vibrations.     

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%.     

Calculation and interpretation of the fine structure fluorescence spectra of anthracene upon resonance excitation of vibronic states

The vibrational structure of the spectra of fluorescence of anthracene obtained upon resonance excitation of vibronic states is calculated and analyzed by the parametric method of the theory of the vibronic spectra of complex molecules. The theoretical and experimental spectra agree qualitatively with each other, which indicates that this method of modeling such spectra is efficient. The parameterization of molecular models obtained upon calculation of the ordinary fluorescence and absorption spectra is completely applicable to the calculation of the fluorescence spectra considered. A total interpretation of the spectra is presented.     

Comparative analysis of intramolecular interactions in trans-stilbene and 1,4-distyrylbenzene

We have analyzed the intensity distributions in fine-structure fluorescence and fluorescence excitation spectra of trans-stilbene in n-hexane at 4.2 K. Modeling the spectra by representing each of the vibronic transitions by a zero-phonon line and a phonon wing with certain parameters (widths, Debye-Waller factors) made it possible to determine relative intensities of vibronic transitions. The parameters of Franck-Condon and Herzberg-Teller interactions, which form the fine-structure spectra of stilbene, have been calculated and compared with previously obtained parameters of intramolecular interactions in 1,4-distyrylbenzene.     

Orientation studies by N.M.R. spectroscopy using a lyotropic liquid crystal solvent

Excitation profile of resonance enhanced Raman lines, due to totally symmetric motions of soluble cis-polyacetylene, show a resolved Frank-Condon structure which reproduces the one in the electronic absorption spectrum. A model calculation which uses two excited electronic states coupled by intra-band vibronic interaction, three vibrational modes, homogeneous and inhomogeneous broadening and a small contribution from pre-resonance states, has been worked out to fit the experimental excitation profiles in the framework of the band model approach like that used for metals in solid state language.     

Analysis of the two-photon absorption spectrum of benzonitrile based on the direct quantum-mechanical calculation of the intensity distribution

A direct quantum-mechanical calculation of the intensity distribution in the two-photon absorption spectrum of benzonitrile is performed taking into account the Herzberg-Teller effect. The excitation mechanism of all the observed lines, including lines corresponding to the excitation of single-quantum nontotally symmetric vibrations and their combinations with totally symmetric modes, is analyzed. The results of the calculation, performed taking into account the frequency effect and the Duschinsky effect, agree satisfactorily with experimental data. This indicates that it is worthwhile to apply the quantum-mechanical method in calculations of the intensity distribution in the two-photon absorption spectra of cyclic molecules.     

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.     

Site-selection optical spectra of bacteriochlorophyll and bacteriopheophytin in frozen solutions

Site-selection spectra of title compounds in different frozen solvents at 5K have been obtained: fluorescence spectra on selective excitation in vibronic as well as in the O-O absorption region and excitation spectra with narrow-band fluorescence recording. Frequencies of vibrational modes active in fluorescence and excitation spectra of bacteriochlorophyll a (BChl) and its metal-free derivative have been determined from these fine-line spectra. Most favourable vibronic line-to-background intensity ratios have been found in non-polar aprotic glassy environments (triethylamine, di-iso-amylether). The intensity of zero-phonon lines in microcrystallic protic matrices was low, indicating strong electron-phonon coupling. The vibrational frequencies of the excited electronic state characteristic of axially (at Mg atom) mono- and disolvated BChl species have been identified. Narrow spectral holes of about 20% of the initial absorption could be burned with ≈10^-4 quantum yield within the O-O band of BChl and bacteriopheophytin.     

Experimental determination and interpretation of fluorescence and fluorescence excitation spectra of 1,2-benzanthracene cooled in supersonic jet

We measured the fluorescence and fluorescence excitation spectra of supersonic jet-cooled 1,2-benzanthracene. Using the MO/M8ST method, we calculated the frequencies of in-plane vibrations in the ground and first excited singlet electronic states, and, in the Franck-Condon approximation, we calculated the intensities of transitions between them. Experimental spectra are interpreted based on these data. In the fluorescence excitation spectrum, the position of the line of the 0–0 transition (26535 ± 1 cm⁻¹), which is the most intense, is determined.     

Fluorescence spectra of anthracene and pyrene in water and in aqueous surfactant solution

The fluorescence and excitation spectra of anthracene and pyrene have been measured in water and in aqueous solution of sodium dodecyl sulfate (SDS), and compared with the spectra in ethanol, for microcrystals and in a solution by the dilution method. The molecular spectra observed in water exhibit large broadenings and red-shifts due to the specific solvent effects of water. In aqueous SDS solution the spectra of anthracene are considerably broadened and red-shifted, suggesting the existence of the molecules near the micellar surface, while in the emission spectrum of pyrene remarkable intensity reductions of the vibronic bands have been observed, indicating a weak polarity of the environment in the SDS micelles.     

Study of vibronic interactions in impurity centers by conjugate fluorescence and absorption spectra with a poorly resolved vibrational structure

The conjugate fluorescence and fluorescence excitation spectra of recently synthesized substituted arylpolyene (C₆H₅-[CH=CH]₂-C₆H₄-NH₂) are studied in solid n-octane at a temperature of 4.2 K. The spectra exhibit a weakly pronounced vibrational structure. A method of determination of the vibronic interaction parameters responsible for the shape of the spectra is developed. The method is based on the modeling of the spectra by series of vibronic bands, each of which consists of a narrow zero-phonon line and a broad phonon wing (phonon sideband). This makes it possible to calculate the fluorescence and fluorescence excitation spectra with the weakly pronounced vibrational structure and compare them with the measured spectra. The deviations from the mirror symmetry between the measured fluorescence and fluorescence excitation conjugate spectra are explained by the combined effect of the Franck-Condon and Herzberg-Teller interactions. The parameters of these interactions are determined.     

Structural form of vibronic intensities in vibronic induced transitions

A general method for calculating the overall shape of the spectrum of vibronic induced transitions in transition-metal ion systems is developed. The vibronic structure is expressed in terms of a weighted sum of medium induced lorentzian lines located at the frequencies of the fundamental odd vibrations of the complex. Each of these lines is followed by a series of vibronic lines assigned to the combination frequencies with one or more even vibrations. The relative intensities of these combination lines are determined by the values of an intramolecular distribution which includes both the effects of geometry and frequency changes of the modes involved in the transition. Values of the linear and the quadratic parameter for the molecule can be estimated from a fit to the experimental spectra.     

Specific features in the vibronic fluorescence spectra of analogues of 1,4-bis(5-phenyl-2-oxazolyl)benzene with oxadiazole and furan rings

The fine-structure fluorescence and fluorescence excitation spectra of conjugated chain compounds, namely, 2,5-bis(5-phenyl-1,3,4-oxadiazol-2-yl)furan (PDFDP) and 2,5-bis[5-(2,4-dimethylphenyl)-1,3,4-oxadiazol-2-yl]furan (XDFDX), were obtained by the Shpolskii method in an n-octane matrix at a temperature of 4.2 K. These spectra were simulated by representing the band of each of the vibronic transitions as the sum of a zero-phonon line and a phonon wing with the corresponding parameters, such as the half-widths of the spectral lines and the Debye-Waller factors. The results obtained made it possible to estimate the relative intensities of the vibronic transitions between the S ₀ and S*₁ states. The anharmonicity revealed in the conjugate spectra of fluorescence and fluorescence excitation of the PDFDP and XDFDX compounds was explained in terms of the interference of the Franck-Condon and Herzberg-Teller interactions occurring in the molecules under investigation. The influence of the substitution of the furan heterocycle (F) for the central benzene ring (P) in 1,4-bis-(5-phenyl-2-oxadiazolyl)benzene (PDPDP) on the parameters of the intramolecular interactions responsible for the formation of the vibronic spectra was considered.     

Improvement of the parametric method of the theory of vibronic spectra of polyatomic molecules: Absorption spectra and the structure of butadiene, hexatriene, and octatetraene in the excited state

The structure of the excited states and absorption spectra of butadiene, hexatriene, and octatetraene are calculated by the parametric method of the theory of vibronic spectra using models of the first-and second-order approximations. It is shown that these molecular models adequately reflect the molecular structure and allow one to predict quantitatively the shape and fine vibrational structure of the absorption spectra. When passing to the second-order approximation, only two additional (angular) parameters are used. These parameters are transferable in the series of polyenes. Compared to the first-order approximation model, the second-order approximation model more accurately takes into account the angular deformations of polyenes upon their excitation and describes the intensity distribution in the vibrational spectrum, including weak lines. In addition, the calculations also quantitatively predict spectral variations in the molecular series. The parametric method is more efficient for modeling polyatomic molecules in the excited states and their vibrational spectra compared to other semiempirical and ab initio methods.     

Single vibronic level fluorescence of CrO2Cl2 excited by a tunable cw dye laser

Fluorescence of gaseous chromyl chloride has been excited using a tunable cw dye laser, and fluorescence spectra have been recorded for excitation in 20 different absorption bands. The vibrational structure of these spectra shows activity of all of the totally symmetric vibrations, but there is no evidence for activity of any non-totally symmetric vibration as previously proposed from absorption spectra. We conclude that the absorption band system near 5800 Å comprises at least two electronic transitions.     

C60三阶微商吸收光谱分析

利用三阶微商吸收光谱观测到了紫外一可见区Ｃ６０更为丰富捐收跃迁结构，基于 伦兹线型假设，实验上拟合确定了相应迁能量和寿命加宽参数，并对跃迁结构进行了初步指认，给出了部分振动模的频率。与常规吸收光谱比较，表明了三阶微商光谱是分析Ｃ６０等团簇光物理特性的有效手段。     

Jet Spectroscopy of theD12B1–D01B1Transition of thep-Cyanobenzyl Radical

We have generated thep-cyanobenzyl radical in supersonic free expansion, and measured the vibrationally and rotationally resolved laser induced fluorescence (LIF) excitation spectra and the LIF dispersed spectra from the single vibronic levels (SVL) in the green-blue region. The lowest energy band at 20 738 cm⁻¹with the strongest intensity in the excitation spectrum has been assigned to the 0⁰₀band of the visible spectrum, on the basis of the vibronic structures in the SVL dispersed spectra. Based on the band type of the 0⁰₀band,a-type, determined from the rotationally resolved LIF excitation spectrum, we have definitely assigned the visible band to theD₁2²B₁–D₀1²B₁electronic transition. We have found, on the grounds of the vibrational analysis of the dispersed spectra, that the vibronic structure of the 2²B₁–1²B₁electronic transition of the benzyl type is characterized by totally symmetric fundamental modes, 1, 8a, and 9a.     

An experimental test of symmetry selection rules in inelastic electron tunneling spectroscopy (IETS)

The inelastic electron tunneling spectrum of a highly symmetric molecule, anthracene, is presented. An analysis of the spectrum shows that the vibrational frequencies as measured by tunneling agree well with optical measurements. The high degree of symmetry of the molecule allows separation of the infrared, Raman, and optically inactive modes. The infrared and Raman active modes have comparable intensities; the optically inactive modes are much weaker. Analysis of these intensities within the framework of existing theories suggests that the coupling of tunneling electrons to the induced dipole moment of molecules is large and cannot be neglected.