Polarized fluorescence of radicals in photodissociation of disulfides in the gas phase

The polarization of the fluorescence of radicals formed in laser-induced photodissociation of some disulfides in the gas phase is measured. Experimental data obtained in the study are interpreted within the free recoil model. It is shown that polarization experiments carried out to investigate photodecay in vapors allow researchers to uniquely the intramolecular direction of the dipole moments of transitions with absorption and emission. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 54–59, January–February, 1999.     

Anisotropy of ensembles of free polyatomic photoisomers

In order to describe the polarization response of an ensemble of molecules undergoing structural transformations (photoisomerization) under collisionless conditions, we have calculated the orientational correlation functions. We assume that changes in molecular structure can be considered as instantaneous on the molecular rotation scale. We have obtained general expressions for the anisotropy when the original molecule and the photoisomer are asymmetric tops. We have performed anisotropy calculations for steady-state experimental conditions and a number of limiting situations, when the characteristic times of the photoreaction are much shorter or much longer than the molecular reorientation times and when the original molecule and the photoisomer are planar tops. We have shown that detecting the polarization response allows us to estimate the characteristic times of the photoreaction and to determine the intramolecular orientation of the transition dipole moments for transitions with absorption and emission of light. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 582–587, September–October, 2006.     

Fluorescence of free complex molecules

A number of phenomena that determine the nature of the fluorescence of free complex molecules and the possibility of its analytical application are considered. Attention is specially paid to the specific features of the energetics of radiationless transitions, the role of statistical factors in the formation of spectral properties and the interrelationship among the luminescence-spectrum characteristics of rarefied vapors of complicated molecules, and the processes of energy transfer in collisions. The properties of polarized fluorescence of hot and jet-cooled vapors, the processes of relaxation of anisotropy in time and during collision reorientation, and transfer of anisotropy in photodisintegration are analyzed. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 620–634, September–October, 1998.     

负离子光致分离实验中多过程问题的讨论

本文定量地讨论了光致离解过程对测量多原子负离子的光致分离截面的影响.并提出了同时测量负离子的光致分离截面、光致离解截面以及碎片的光致分离截面的可能性.     

Collisional depolarization of fluorescence of polyatomic molecules in the gas phase by excited state quenchers

A new method of extracting information on the efficiencies of quenching of an excited state and collisional reorientation from the data on the fluorescence depolarization of molecular vapors by quenchers of the excited state is proposed. The method does not involve collisional cross sections and fluorescence lifetimes. From the experimental data on the depolarization of polarized luminescence of para-quaterphenyl and 2-(4′-dimethylamine) phenyl-5-phenyloxydiazole by oxygen and nitrogen, the ratios of the constants of the excitedstate quenching and orientation randomization (fluorescence depolarization) by oxygen are obtained. For these molecules, the probabilities of the excited-state quenching q and orientation randomization s per collision with oxygen molecules are determined (q=0.25±0.04 and s=0.13±0.04 for para-quaterphenyl and q=0.2±0.04 and s=0.21±0.04 for 2-(4′-dimethylamine)phenyl-5-phenyloxydiazole). The self-quenching of fluorescence of perylene vapors, with the probability 0.28 per collision, is found.     

Formation of fluorescence bands of polyatomic organic molecules in the gaseous phase upon excitation by electrons

Information on paths in absorption and deactivation of energy gained by molecules in their excitation by electron impact to low-lying singlet states has been obtained from an analysis of changes in the fluorescence spectra of these molecules. It is shown that there is a significant difference in the formation of fluorescence spectra when free molecules are excited by optical radiation and by electrons. It contrast to optical excitation, the interaction of an electron with a molecule is nonselective in character. All electronic states have a chance to be excited, which results in ensembles of emitting molecules with a different store of vibrational energy, and these ensembles each contribute to the fluorescence spectrum. Deceased. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 216–223, March–April, 1998.     

用偏振荧光光谱表征乙醇-水团簇分子的取向行为

采用波长为236nm紫外光激励乙醇水溶液获得荧光光谱并对其偏振特性进行了研究.实验中分别改变入射光的偏振度，在300—400nm波段内进行荧光光谱、水平和垂直偏振荧光光谱检测.实验结果表明，当采用线偏振光照射乙醇水溶液时，其发射的荧光具有一定的偏振性，并计算了其偏振度.经理论分析得到了描述荧光偏振态的四个斯托克斯矢量，进而对该荧光的偏振状态进行了描述，通过对乙醇-水溶液的米勒矩阵的计算，对溶液中分子的取向特性进行了分析.本结果能对乙醇-水团簇分子的结构提供理论参考. 关键词： 荧光光谱 偏振光谱 斯托克斯矢量 米勒矩阵     

Myosin head rotation in muscle fibers measured using polarized fluorescence photobleaching recovery

The technique of polarized fluorescence photobleaching recovery (PFPR) has been applied for the first time to investigation of the rotational correlation time of the myosin head in muscle fibers. This is a novel application of PFPR because it is the first time PFPR has been applied to a sample which is not cylindrically symmetric about the optical axis. Therefore we present a method for analysis of PFPR results from an oriented sample such as the muscle fibers aligned perpendicularly to the optical axis used here. Control experiments performed on fluorescently labeled myosin heads in solution demonstrate that, under some conditions, our PFPR apparatus can easily measure a rotational correlation time of less than 200 s. Validity of this application of PFPR to muscle fibers is provided by the agreement of our results with published results from a variety of other spectroscopic techniques. In particular, using glycerinated rabbit psoas muscle fibers, we find that for relaxed fibers and isometrically contracting fibers, the myosin heads undergo high-amplitude rotations on the submillisecond time domain. For fibers in rigor the myosin heads are highly oriented and nearly immobile. For fibers in ADP the myosin heads are highly ordered in a distribution quite different from that in rigor, and they are slightly more mobile than in rigor.     

Luminescence of complex organic molecules upon electron excitation

Pesults of investigation of the luminescence of complex organic compounds upon excitation with electrons of various energies are reported. Data on spectra of energy losses of electrons, fluorescence excitation cross sections and functions, fluorescence emission spectra, fluorescence kinetics, polarization, and energy yield, effects of impurity gases, and theoretical analysis of the processes taking place in the system are presented. Results of investigation of the luminescence of complex molecules in electric discharges (dc, pulsed, high-frequency, non-self-maintained, and plasma-beam) and in a condensed state (solutions, molecular crystals, and thin solid films) are discussed. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk 220072, Belarus. Transtated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 694–708, September–October, 1998.     

Femtosecond Dynamics of Optically Induced Anisotropy of Complex Molecules in the Gas Phase

The evolution of optically induced anisotropy in an equilibrium ensemble of free asymmetric tops under collisionless conditions has been investigated theoretically and experimentally. The dynamics of the orientation correlation functions has been studied, the results of femtosecond experiments on measurement of relaxation of the optically induced anisotropy for perylene in the gas phase are presented, and their interpretation within the framework of the theory developed is given. It is shown that in contrast to stationary anisotropy, its time kinetics has more complete characteristic information about the dynamics of vector correlations in a molecular ensemble.     

New quasiparticles hystons and coherent photoinduced dynamics of molecules in polar disordered media

Using methods of statistical thermodynamics, it is shown that after pulse excitation the evolution of a “polar luminescent probe—polar disordered medium” system is described by an equation of damping vibrations. This allows the conclusion that in the solvate shell of the probe molecule synchronous rotational vibrations (librations) of the molecules of the medium occur, whose damping is caused by dielectric friction. Such a collective synchronous motion is considered as a motion of a quasiparticle called a hyston. The moment of inertia J_n and mass M_h of a hyston are defined as J_h=2m² ₁a^-3Ω₀ ^-2(ε-1)/(2ε+1), M_h=J_hM_s/J_s, where m₁ is the dipole moment of the probe molecule in the excited S₁-stute; a is the Onsager radius; Ω₀ is the cyclic frequency of harmonic vibrations of the hyston; ε is the dielectric constant; M_s and J_s are the mass and moment of inertia of a molecule of the medium, respectively. The correlation function of the motion of the molecules c(t) is a solution of the equation of hyston motion. The fluorescence response s(t) in measurements with time resolution coincides with the correlation function: s(t)=c(t). The concepts concerning hystons make it possible to describe macroscopic photoinduced coherent motion that is manifested against a background of thermal motion of the medium molecules. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnei Spektroskopii, Vol 65, No. 2, pp. 176–183, March–April, 1998.     

Quenching of fluorescence of porphyrin molecules in their association in binary solutions

It has been established that the absorption and fluorescence spectra of octaethylporphin (OEP), mesotetraphenylporphin (TPhP), and its complex with zinc (Zn-TPhP) in glycerol doped with dimethylformamide (DMF) or ethanol differ from the analogous spectra of these compounds in ethanol or DMF, which is due to the formation of associates of porphyrin molecules in solutions of OEP, TPhP, and An-TPhP with glycerol. For TPhP and Zn-TPhP, these differences are small, the maxima of the bands are shifted toward longer wavelengths by 3–5 nm, and their halfwidths are increased by ∼ 16%; for OEP these changes are more significant. It is shown that the duration of fluorescence of associates is much shorter than that of monomers. The probable mechanisms of quenching of the fluorescence of dimers (oligomers) of molecules were considered. It has been suggested that one of the reasons for the increased rates of deactivation of the excited states of dimers (oligomers) may be the decreased energy interval between the excited and ground states of associates as compared with that of monomers. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 21–25, January–February, 2000.     

Production of cold CN molecules by photodissociating ICN precursors in brute-force field

We theoretically investigate the production of cold CN molecules by photodissociating ICN precursors in a brute-force field. The energy shifts and adiabatic orientation of the rotational ICN precursors are first investigated as a function of the external field strength. The dynamical photofragmentation of ICN precursors is numerically simulated for cases with and without orienting field. The CN products are compared in terms of their velocity distributions. A small portion of the CN fragments are recoiled to near zero speed in the lab frame by appropriately selecting the photo energy for dissociation. With a precursor ICN molecular beam of ～ 1.5 K in rotational temperature, the production of low speed CN fragments can be improved by more than 5 times when an orienting electrical field of 100 k V/cm is present. The corresponding production rate for decelerated fragments with speeds ≤ 50 m/s is simulated to be about ～2.1×10~(-4) and CN number densities of 10~(8) –10~(10) cm~(-3) can be reached with precursor ICN densities of ～10~(12) –10~(14) cm~(-3) from supersonic expansion.     

Monatomic rarefied gas as a singular limit of polyatomic gas in extended thermodynamics

We show that, in the theory of extended thermodynamics, rarefied monatomic gases can be identified as a singular limit of rarefied polyatomic gases. Under naturally conditioned initial data we prove that the system of 14 field equations for polyatomic gases in the limit has the same solutions as those of the system of 13 field equations for monatomic gases where there exists no dynamic pressure. We study two illustrative examples in the process of the limit, that is, the linear waves and the shock waves in order to grasp the asymptotic behavior of the physical quantities, in particular, of the dynamic pressure.     

Absorption,fluorescence, and fluorescence excitation spectra of free molecules of indole and its derivatives

We have obtained and analyzed the absorption, fluorescence, and fluorescence excitation spectra of indole vapor, N-acetyl-L-tryptophan vapor, and 3-indole aldehyde vapor. From analysis of the dependence of the fluorescence spectrum of the free indole molecules on the wavelength of the exciting radiation λ_ex, it follows that emission of fluorescence occurs when the molecules undergo a transition from the one electronically excited state ¹L_b. The fluorescence spectra of the studied compounds are insignificantly different, suggesting a major role for the indole chromophore in formation of the compounds. The absorption spectrum of N-acetyl-L-tryptophan, in which the group of atoms is added to the indole ring through a-C-C bond, is similar to the spectrum of indole, while the spectrum of 3-indole aldehyde is significantly different from the indole spectrum due to the effect of the C=O group conjugated with the indole ring. The fluorescence excitation spectra are considerably different from the absorption spectra. This is associated with the strong dependence of the quantum yield for the free molecules on λ_ex. Qualitatively, they are mirror-symmetric to the fluorescence spectra of the stodied compounds. Analysis of the data obtained provides a basis for assuming that in the case of free molecules of indole and its derivatives, the ¹L_a absorption in the extreme long-wavelength region of the spectrum does not overlap ¹L_b absorption. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 218–222, March–April, 2007.     

Photophysical Processes in the Gas Phase at High Levels of Vibrational Excitation of Triplet Molecules of Benzophenone and Fluorenone

By the delayed fluorescence activated by direct multiphoton excitation of triplet molecules by CO₂–laser radiation we have studied the prevailing deactivation pathways of triplet molecules with a high store of vibrational energy E _vib. The dependences of the kinetic characteristics of delayed fluorescence on the presence of vapors and foreign gases have been used to estimate the rates and efficiencies of intermolecular vibrational relaxation in the vibrational quasi–continuum of the triplet state T ₁. By the changes in the intensities and decay rates over a wide range of vibrational energies we have established the E _vib dependences of reversible intercombination conversion between the states T ₁ and S ₁ and interconversion from T ₁ to the ground electronic state S ₀ for both the case of isolated excited molecules and at a steady vibrational temperature. It is shown that at high vibrational temperatures the radiationless transition from the T ₁ state to S ₀ has an activation character and is accomplished through the energy barrier. The conditions for going to an exponential dependence have been determined. It has been found that the obtained dependences are in good agreement with the known experimental results. The influence of molecular and environmental characteristics on the decay rate of triplet molecules is compared.     

Absorption and fluorescence of 8-azasteroids in the gas phase

Extensive studies of the spectral-luminescent characteristics of four 8-azasteroids and a model compound 2-(3,3-dimethyl-1,2,3,4-tetrahydro-1-isoquinolidene)-5,5-dimethyl-1,3-cyclohexanedion in the gas phase have been made. From the analysis of the dependences of the absorption spectra on the vapor pressure (T_low) and the fluorescence spectra on T_low and the exciting radiation wavelength (_exc) a conclusion on the presence in the vapors of the investigated 8-azasteroids of three absorption and fluorescence centers (S-, M-, and L-centers) has been drawn. The absorption spectra of these centers strongly overlap. Their long-wave absorption boundaries have been determined. The dependence of the fluorescence spectra of all three centers on _exc, which is inherent in rarefied gases of individual organic molecules, is observed. The S-centers are the molecules of the initial steroids, and the M- and L-centers are the molecules of thermo- and phototransformations of the initial steroids. The model compound in the gas phase is characterized by the same dependences of the fluorescence spectra on T_low and _exc as those inherent in 8-azasteroids. Taking into account the additional data obtained as a result of investigation of the absorption and fluorescence spectra of solutions of the substances extracted from vacuum cells after the investigation of 8-azasteroids and the model compound in the gas phase, conclusions on the nature of the M- and L-centers have been drawn.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 48–57, January–February, 2005.     

Monatomic gas as a singular limit of polyatomic gas in molecular extended thermodynamics with many moments

The difference in the theoretical structure between monatomic and polyatomic gases in highly nonequilibrium states is discussed from the viewpoint of molecular extended thermodynamics (MET) of rarefied gases, which is free from the local equilibrium assumption. The MET theories of these two types of gases are based on the moment balance equations with different hierarchy structures due to whether the internal degrees of freedom of a molecule are incorporated in their distribution functions or not. In particular, the number of balance equations in the MET theory of polyatomic gases is greater than the number in the corresponding theory of monatomic gases. The closure procedure for the system of balance equations of polyatomic gases obtained in a recent paper (Arima et al., 2014) is adopted. We prove that the solutions for polyatomic gases converge, in the limit where the degrees of freedom of a molecule D$D$ tend to 3, to the ones for monatomic gases provided that we impose appropriate initial conditions compatible with monatomic gases. Thus a MET theory of rarefied monatomic gases can be identified as a singular limit of the corresponding MET theory of rarefied polyatomic gases. As illustrative examples, the asymptotic behaviors when D→3$D\to 3$ in the dispersion relation of ultrasonic waves and in the shock wave structure are shown.