Anomalous vibrational relaxation of a hot S*1 state of 3,4-benzpyrene in 2-methylpentane

Two anomalous emission bands in the fluorescence spectrum of 3,4-benzpyrene, dissolved in 2-methylpentane, have been studied as a function of temperature. These emissions originate from the second excited singlet state S₂, and from a vibrationally excited S₁ (S^*₁) respectively. From the temperature dependence of the relative yield and the decay time of the S^*₁ emission it can be concluded that the vibrational relaxation of this state is hampered. The rate constant for this relaxation process is smaller that 4 > 62;x 10⁷ sec^?1.     

Dual fluorescence (S1, S2) in chrysene and 3,4-benzophenanthrene

S₂ and S₁ fluorescence of chrysene and 3,4 benzophenanthrene has been observed in the vapour phase under collision free conditions. It is shown that the intermediate strong couplinng model can be applied to these molecules. The efficiency of the transfer of the excess energy to collision partners is given for different gases.     

Fluorescence decay of pyrene vapour; biphotonic excitation and the kinetics of vibrational redistribution

A computer simulation procedure has been applied to the fluorescence decay curves of pyrene vapour, excited into the S₁ state with short laser pulses. The results confirm that the kinetic model which has been used previously in order to describe the effect of vibrational redistribution on the fluorescence decay, is consistent with the experimental decay curves. A very short decay component (τ ≈ 4 nsec) which appears when the energy of the laser exceeds 1.5 mJ is ascribed to doubly excited pyrene molecules.     

On the lower excited electronic states of glyoxal

The polarization of both nπ* absorption bands of glyoxal has been measured in a glass matrix of 2-methyltetrahydrofuran by the photoselection method. The second absorption band in the 30 000 cm^?1 region has been assigned to a ¹A_g → ¹B_g nπ* transition. Its intensity is mainly induced by interaction with the solvent. An absorption band at about 43 000 cm^?1 has been ascribed to a charge transfer transition in complexes of glyoxal and 2-MTHF.     

Molecules in molecules calculations on decacyclene

The calculation of the ring-current contribution to the proton chemical shifts in conjugated systems using uncoupled Hartree-Fock perturbation theory is improved by the inclusion of origin variation in the expression for the vector potential.     

Franck-Condon factors of the torsional mode ν7 in the SVL emission of glyoxal

Drastic changes occur in the intensity pattern of the emission spectra of the 7ⁿ-levels as compared to the spectrum of the 0⁰-level. These changes are due to greatly enhanced intensity of the sidebands in the progression of the 7-vibration. This enhancement is, in a first approximation, in agreement with calculations of the Franck-Condon factors of these transitions. The additional intensity of the sidebands in the emission from the 7²-level can be explained in part by intensity borrowing from the 5¹-emission due to a coupling of the 7² and 5¹-levels. The large relative intensities of the 7₅², 7₅³, and 7₇³ emission bands remain unexplained.     

The relative S*1 emission yield of 3,4-benzpyrene in the vapour phase

The relatives S^*₁ emission yield as a function of excitation energy can be interpreted as arising from an ensemble in which the excess energy is randomly distributed over the vibrational modes.     

Induzierte Ultrarotabsorption im Spektralgebiet der ersten Oberschwingung von Wasserstoff

Pressure induced absorption has been investigated in mixtures of H₂ with CF₄, SF₆, N₂, CO₂ and N₂O respectively, in the frequency region 8000–9500 cm^?1 of the first overtone of H₂. In mixtures of H₂ with CF₄ or with SF₆ simultaneous vibrational transitions are observed. The absolute intensities of the induced 0→2 vibrational transition of H₂ in the different mixtures and of the simultaneous transitions have been evaluated. Formulas are derived for the absolute intensity of those induced transitions. The induction of the simultaneous transitions is mainly due to the electrostatic interaction in the collision pairs. The contributions of the electrostatic forces and of the overlap forces are of the same order of magnitude in the case of the induced 0→2 vibrational transition of H₂.     

Vibrational relaxation and intermediate strong coupling

In this paper the effect of collisions with inert gas molecules upon the intermediate strong coupling situation, found in the fluorescence of isolated pyrene molecules after pulse laser excitation in the S₀ → S₃ absorption band, is studied.     

Determination of the barrier to intramolecular exciplex formation in a jet-cooled, bichromophoric molecule

The emissive properties of a bichromophor molecule (1) are reported. This contains an anilino group as an electron donor (D) and a 1-cyanonaphthalene group as an electron acceptor (A) interconnected by a saturated hydrocarbon bridge of limited flexibility, which holds D and A far apart in the electronic ground state. The emission spectrum of 1, both in solution and in the gas phase, indicates that quantitative formation of an intramolecular exciplex between D and A occurs. This exciplex formation was studied as a function of excitation energy in molecules of 1 isolated in a supersonic free jet. A barrier of 1700 ± 200 cm⁻¹ was found between the Franck-Condon excited conformation and the conformation of the exciplex. Although this value is significantly higher than that reported earlier for exciplex formation between chromophores connected by a simple polymethylene chain (≈ 900 cm⁻¹) it is much lower than the barrier predicted for folding the bridge in 1 sufficiently to bring D and A in close contact. A tentative explanation of this discrepancy is given.