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.     

The fluorescence excitation spectrum of s-tetrazine cooled in a supersonic free jet

The fluorescence excitation spectrum of the ${}^1\text{B}{}_{\mathrm{3u}}\text{(v′ = 0) ←}{}^1\text{A}{}_{\mathrm{g}}\text{(v″ = 0)}$ transition in s-tetrazine has been observed and measured. The sample was cooled to a rotational temperature of <1 K by expansion in a supersonic free jet. In this way the rotational structure arising from asymmetry split low J lines could be observed. The rotational A and B axes of the ²H₁¹²C₂¹⁴N₄ isotope were observed to interchange upon electronic excitation and a theory describing the effect of this interchange upon the optical selection rules has been developed. Analysis of the resolved rotational structure suggests that the geometry change upon electronic excitation is smaller than that deduced from previous analysis of the room temperature optical spectrum.     

Effect of saturation on vibro-rotational contours in the excitation spectrum of quinizarin cooled in a supersonic jet

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 3, pp. 449–456, September, 1990.     

Comparative analysis of high-resolution spectra of naphthalene and its methyl-substituted derivatives cooled in a supersonic jet

We have carried out a comparative analysis of fine-structure fluorescence excitation and fluorescence spectra of naphthalene, 2,6-and 2,7-dimethylnaphthalene, and 2-methylnaphthalene molecules cooled in a supersonic jet. We have shown that both the frequencies and the intensities of most of the lines in the spectra of these molecules are correlated. Such a correlation facilitates interpretation of the spectra in the case when it is difficult to calculate the transition intensities and when lines corresponding to vibrations of different symmetry have close frequencies. For the considered molecules, a preliminary assignment of the lines in the fine-structure spectra is refined. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 336–340, May–June, 2007.     

Fluorescence polarization of helical molecules cooled in a supersonic jet

The β-binaphthylene oxide molecules studied under supersonic cooling conditions have a number of specific properties due to their nonplanarity. Low-frequency vibrations of the molecules in the excited S1 state are higher than the frequencies for the S0 state, and conversely the high-frequency vibrations have lower frequencies. The S₀-S₂ fluorescence excitation spectrum is structureless. The absence of a Q branch in the rotational contour of the line for the purely electronic transition indicates that it is substantially broadened and shifted toward shorter wavelengths as a result of rotational perturbations of the helical structure of the molecule. Multiplet lines in the spectra of β-binaphthylene oxide complexes with argon, krypton, and xenon correspond to different isomeric complexes. Their bond energies are below those observed previously for planar polycyclic molecules such as perilene, fluorene, and carbazole. The greater number of isomers with xenon is due to strengthening of the bond in the van der Waals complex and the nonequivalence of the position of the xenon atoms on the outside and inside of the helical molecule. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 473–477, July–August, 2006.     

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.     

Manifestations of the saturation effect in the polarization of the fluorescence of quinizarin molecules cooled in a supersonic jet

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 4, pp. 567–572, October, 1990.     

1-甲基萘的振动分辨激光诱导荧光光谱研究

在超声射流条件下得到了1-甲基萘的激光诱导荧光光谱,并结合理论计算研究了1-甲基萘分子的基态和激发态的几何构型及振动信息.运用DFT方法在B3LYP/6-311++G*的水平上优化了1-甲基萘的基态儿何构型,结果表明1-甲基萘分子基态的S-E和E-S两个构象体中,只有S-E构象体为稳定构型,E-S构象是连接两个S-E构...     

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.     

Rotational contours of electronic and electronic-vibrational bands of carbazole complexes with water cooled in a supersonic jet

The rotational contours of the bands corresponding to electronic and electronic-vibrational transitions of the fluorescence excitation spectrum of jet-cooled carbazole complexes with one, two, and three water molecules have been studied. For the carbazole-(H₂O)₁ complex, two bands with a spectral shift of 0.57 cm^?1 were recorded under exposure to radiation with a spectral width of 0.08 cm^?1 at the frequency of the purely electronic transition and some other electronic-vibrational transitions. This is caused by the tunnel effect. The intensities of the shifted low-frequency bands are threefold weaker than those of high-frequency bands due to different values of nuclear spin-statistical weights. In the carbazole-(H₂O)₂ and carbazole-(H₂O)₃ complexes, water molecules are combined into a chain by the hydrogen bond, and the two ends of the chain are hydrogen-bonded to the carbazole molecule. The principal axes I _A and I _B of the moments of inertia in carbazole-(H₂O)₃ have different orientation compared to the other complexes considered, and this leads to an increase in the intensity of the Q-branch.     

Molecular structure of trimethyl[(3-indole)ethoxy]silane cooled in a supersonic jet

Conformations of He-jet-cooled trimethyl[(3-indole)ethoxy]silane (TIES) have been studied using a laser spectroscopy technique in combination with quantum-chemical computations. Six probable conformers of the molecule were computed, of which only two conformations were observed. Based on an analysis of fluorescence excitation spectra, fluorescence spectra, shapes of rotational band contours at the electronic S₀–S₁ transition of TIES, and theoretical computations, the above conformers were assigned to steric structures. Twisted structures have the lowest energy due to intramolecular hydrogen bonds C - H ?O < _C^Si C - H \cdots O <_C^{Si} between hydrogen atoms of methyl groups and an oxygen atom and C–H···π between H and the π-electron cloud of the indole ring.     

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%.     

Determination of the kinetic coefficients of a gas in a supersonic jet from Brillouin spontaneous scattering spectra

The mean free path and the shear viscosity of molecular nitrogen are determined in a rarefied supersonic jet using the Brillouin spontaneous scattering technique. By examples of sub-and supersonic jets, the measured kinetic coefficients are shown to agree with the tabulated values of these parameters. These results are obtained using laser radiation, whose output power, which restricts the signal-to-noise ratio, is as low as 50 mW.     

Computer simulation of multiphoton excitation of SF6 molecules cooled by pulsed supersonic expansion

The initial ground-state dependence of the multiphoton excitation of SF₆ is numerically estimated using two different approximations for thev ₃ vibration-rotation levels and for the laser line width. From this calculations we have identified and explained some features seen in recent experimental data.     

Fermi-type resonance in quasi-linear fluorescence excitation spectra of triazatetrabenzoporphine

The effect of deuteration of the central NH groups on the quasi-linear fluorescence and fluorescence excitation (with selective monitoring) spectra for triazatetrabenzoporphine, a close analog of phthalocyanine, has been investigated at 77K in n-nonane. Vibrational analysis of the spectra was carried out. The normal mode frequencies were determined for the electronic states S₀ (from fluorescence spectra) and S₁ (for fluorescence excitation spectra). It has been established that N-deuteration lowers the frequency of a vibration involving inplane NH bending down to ∼990 cm⁻¹ and leads to resonant vibrational-electronic (vibronic) interaction of Fermi-type resonance between the zero level of the S₂ state and the vibronic level of the S₁ state upon excitation of this mode. Thereby the possibility of the “vibronic analog of Fermi resonance” (a term coined by G. Herzberg) occurring in a simple (two-component) variant of phthalocyanine-type molecules has been shown. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 796–803, November–December, 2008.