Bimolecular gas-phase processes with the participation of vibrationally excited triplet molecules of aromatic ketones

Time-resolved moderated luminescence of aromatic ketones (benzophenone, aceptophenone) in the presence of neutral and reactive hydrogeneous foreign gases (ethylene, pentane, triethylamine) is investigated. It is shown that the addition of hydrogeneous foreign gases leads to strong quenching of the triplet molecules of aromatic ketones. Effectivenesses of such bimolecular processes as the collision detachment of a hydrogen atom and establishment of vibrational and thermal equilibrium are compared. It is concluded that the vibrational degrees of freedom of the acceptors, the aromatic ketones, are inactive in the photochemical process of collision detachment of a hydrogen atom that takes place after the establishment of vibrational equilibrium. 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. 73–77, January–February, 1999.     

Lattices of partially local fitting classes

This article deals only with finite groups. We prove the surjectivity of the mapping from the lattice of all normal Fitting classes into the lattice of the Lockett section generated by the Fitting classes that are not Lockett classes. Moreover, we find a sufficient surjectivity condition for the mapping of the lattice of the Lockett section generated by arbitrary Fitting classes into the lattice of the Lockett section generated by ω-local Fitting classes. This confirms Lockett’s conjecture for the ω-local Fitting classes of a given characteristic.     

Fluorescence quenching of vaporous polycyclic aromatic hydrocarbons by oxygen

The fluorescence quenching by oxygen of vapors of nine polycyclic aromatic hydrocarbons with strongly different oxidation potentials 0.44 eV < E _ox < 1.61 eV (anthracene, 9-methylanthracene, 2-aminoanthracene, 9,10-dibromanthracene, pyrene, chrysene, phenanthrene, fluoranthene, and carbazole) is studied. From the dependences of the fluorescence decay rates and intensities on the oxygen pressure P _O2, the quenching rate constants k _S ^O2 for the excited singlet states S ₁ and the fraction f _S ^O2 of the S ₁ states quenched by oxygen are estimated. At P _O2 = 5 Torr, the k _S ^O2 constants vary from 1.2 × 10⁷ to 3.0 × 10⁵ s^?1 Torr^?1, while the fraction of the quenched excited singlet states changes from 0.1 (fluoranthene) to 0.7 (chrysene) and 0.8 (pyrene). The dependences of k _S ^O2 on the photophysical and electron-donor characteristics of the fluorescing compounds are analyzed. It is shown that, in the gas phase of anthracene and its derivatives, the magnitudes of k _S ^O2 are limited by the rate constants of gas-kinetic collisions k _gk and do not depend on the electron-donor characteristics of fluorophores, while the fraction of quenched states f _S ^O2 changes with the oxidation potential. For compounds with k _S ^O2 < k gk, both the rate constants k _S ^O2 and the fraction of quenched states f _S ^O2 depend on the E _ox of sensitizers, which demonstrates an important role played by the charge-transfer interactions in quenching of the S ₁ states. The dependence of the rate constants k _S ^O2 on the free energy of electron transfer ΔG _et is considered.     

Fluorescence spectra of blood plasma treated with ultraviolet irradiation <Emphasis Type="Italic">in vivo</Emphasis>

We have studied the fluorescence spectra of blood plasma from patients with acute coronary syndrome, and also the effect of therapeutic doses of in vivo ultraviolet blood irradiation (UBI) on the spectra. We have established that the maxima in the fluorescence spectra of the original plasma samples, obtained from unirradiated blood, are located in the wavelength interval 330–340 nm, characteristic for the fluorescence of tryptophan residues. In extracorporeal UBI (λ = 254 nm), we observed changes in the shape and also both a blue and a red shift in the maxima of the fluorescence spectra, differing in magnitude for blood plasma samples from different patients in the test group. We show that UBI-initiated changes in the fluorescence spectra of the plasma depend on the original pathological disturbances of metabolite levels, and also on the change in the oxygen-transport function of the blood and the acid–base balance, affecting the oxidative stability of the plasma. We have concluded that UV irradiation, activating buffer systems in the blood, has an effect on the universal and specific interactions of the tryptophan residue with the amino acid residues and water surrounding it.     

Effect of <Emphasis Type="Italic">in vivo</Emphasis> irradiation of blood by low-intensity emission from a He–Ne laser on molecular components of blood

We have used the IR absorption spectra of blood, plasma, and packed erythrocytes to study the effect of in vivo exposure of blood to low-intensity emission from a He–Ne laser (λ = 632.8 nm, 4 mW/cm²) on the molecular components of blood. In comparing the IR spectra of samples of blood sample and blood components before and after irradiation, we identified changes in the amide A, amide I, amide II, amide III absorption regions and also in the absorption bands of methyl, methylene, and phosphate groups. We conclude that exposure of blood in vivo to emission from a He–Ne laser leads to a decrease in the contribution of the α-helix conformation in the secondary structure of the blood proteins.     

Photoinduced Electron Transfer From Carbazole to Halomethanes in a Gas Phase

Intermolecular photoinduced electron transfer (PET) in a gas phase was studied using carbazole vapor fluorescence quenching by halomethanes (CHCl₃, CH₂Br₂, CCl₄, CHBr₃). The fluorescence quenching rate constants k _q changing from 2.3·10⁵ sec^–1·torr^–1 in mixtures with CHCl₃ to 4.6·10⁶ sec^–1·torr^–1 in mixtures with CHBr₃ at a constant temperature of 403 K were estimated. The dependence of the carbazole fluorescence decay rates in the presence of halomethanes on the free energy change G during transfer of the electron from carbazole to halomethanes is considered. It is suggested to take into account the influence of the vibrational energy of the carbazole molecule E _vib and its temperature changes in estimation of the G values. The differences between PET in the gas and liquid phases were analyzed. It is found that for mixtures with CCl₄ and CHBr₃ the negative temperature dependence of k _q is observed, when the decay rates and efficiencies of the intermolecular PET decreased with temperature increase in the range 403–573 K, i.e. these mixtures the electron transfer is not a barrier-restricted process.     

Intermolecular Vibrational Relaxation in Mixtures of Excited Benzophenone and Anthraquinone Molecules with Water Vapor

The intermolecular vibrational energy transfer from triplet molecules of benzophenone and anthraquinone to H₂O molecules has been investigated. To determine the rates of establishment of vibrational (V-V) and thermal (V-T) equilibrium in a vibrational quasi-continuum of mixed singlet-triplet levels, the dependences of the decay rates and intensities of the fast and slow components of delayed fluorescence on the H₂O vapor pressure have been investigated. For V-V relaxation, the efficiencies ₁ and the mean energies E transferred per collision in mixtures with H₂O and other polyatomic foreign gases have been compared. It has been established that the efficiencies ₁ for quasi-resonant vibrational energy transfer (V-V) from benzophenone and anthraquinone to H₂O are an order of magnitude lower than the gas-kinetic ones and lower than those obtained under the same experimental conditions for such foreign gases as C₅H₁₂, SF₆, and CCl₄, and decrease with increasing temperature in the 433–513 K range. It has been concluded that the mechanism of V-V relaxation in mixtures with H₂O are determined by long-range attractive forces. In mixtures with H₂O, no acceleration of V-T relaxation due to the formation of hydrogen bonds has been revealed. The low-efficiency thermalization process (V-T relaxation) is controlled by short-range repulsive forces, and the differences between the intensities ₂ for mixtures of benzophenone and anthraquinone with H₂O and other polyatomic gases are determined by the change in the reduced mass of interacting molecules.     

Triplet-triplet transfer of electronic energy upon nonequilibrium vibrational excitation of triplet molecules

The specific features of the triplet-triplet (T-T) transfer of electronic excitation energy in a gas phase upon nonequilibrium vibrational excitation of the triplet molecules of a donor were studied for an anthraquinone-diacetyl donor-acceptor pair using the time-resolved slow fluoresence of anthraquinone and sensitized phosphorescence of diacetyl. It is shown that in the gas phase, which allows regular control of the number of collisions, competition between the processes of T-T transfer and intermolecular vibrational relaxation is observed for nanosecond time resolution. The T-T transfer rate for the molecular system investigated exceeded the rate of intermolecular vibrational relaxation k_V in the triplet state T₁ of the donor. The effectiveness of the T-T transfer of energy by vibrationally excited molecules turned out to be higher than the effectiveness of transfer by thermalized ones, but even the highest of them was much less than unity. An increase in the equilibrium temperature of vapors led to a decrease in the effectiveness of transfer for both vibrationally excited and thermalized triplet molecules, thus indicating the importance of the collisional complex in the intermolecular process studied. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 474–479, July–August, 2000.