O. Benoist D'Azy

Université Paris-Sud 11, Orsay, Île-de-France, France

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Publications (9)15.95 Total impact

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    ABSTRACT: The fluorescence properties of two biaryl donor-acceptor compounds (4-dimethylamino-4′-cyanobiphenyl (DMACNB) and 4-dimethyl-anilino-1-cyanonaphthalene (DMACNN)) were compared in solvents of different polarity. Low temperature, steady state spectra were also studied in non-polar and polar media. The transient Stokes shifts measured with 30 ps excitation in 1-propanol and 1-hexanol at room temperature show that the charge transfer process is controlled by the dynamics of solvation. A large decrease in the radiative rate constant as a function of the solvent polarity and as a function of time in 1-hexanol solution was observed for DMACNN, whereas this effect was not significant in the case of DMACNB. These differences have been related to the larger steric hindrance to coplanarity in the phenylnaphthalene derivative with respect to that in the substituted biphenyl.
    No preview · Article · Aug 1995 · Journal of Photochemistry and Photobiology A Chemistry
  • P.G. Fournier · J. Fournier · B. Bellaoui · O.Benoist d'Azy · G. Taieb
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    ABSTRACT: Polycrystalline clean Mg has been bombarded by 5 keV Kr+ ions under few 10−6 Torr ultra pure oxygen partial pressure. The well resolved optical spectrum of molecular sputtered particles observed in the 480–501 nm region is attributed to the MgO B1Σ → X1ΣΔv = 0 transition. Computer simulations allow the determination of rotational and vibrational temperatures Trot = 1750 K and Tvib = 5000 K for the sputtered MgO molecules. The previous reported emission in the 480–520 nm region was observed only with contaminated oxygen.
    No preview · Article · May 1993 · Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
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    ABSTRACT: We have observed the time dependence of the motion of the atoms in a van der Waals complex (HgAr). This motion leads to direct dissociation or corresponds to vibrations in the potential well. The time evolution is similar to that observed in the femto-second domain for chemically bound molecules, i.e. it leads to appearance of transients and vibrational recurrences. In softening the potentials, the characteristic time for the movements of the atoms is slowed down to the picosecond. We have observed and analyzed the direct dissociation and the vibrational recurrences in the B potential well.
    No preview · Article · Dec 1992 · Chemical Physics Letters
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    Full-text · Article · Jan 1992 · Laser Chemistry
  • V. Lejeune · A. Despres · B. Fourmann · O. Benoist D'Azy · E. Migirdicyan
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    ABSTRACT: Fluorescence decays of mesitylylene-h10 and -d10 (M-h10 and M-d10) biradicals and mesityl-h11 and -d11 monoradicals are measured between 10 and 77 K. These fragments are generated "in situ" by UV photolysis of mesitylene dispersed in Shpolskii matrices or in glasses. While the fluorescence decay is a single exponential for monoradicals, it is a sum of two exponential functions for biradicals in the whole temperature range between 10 and 77 K. The lifetimes of the two components are 30 ± 6 and 195 ± 15 ns for M-h10 and 50 ± 10 and 265 ± 20 ns for M-d10. These lifetimes are independent of variations in excitation and observation wavelengths, temperatures below 40 K, and local environmental conditions. They are, however, significantly altered in the presence of a 450-G magnetic field. One possible interpretation of these results is to attribute the biexponential decay to the fluorescence from two individual sublevels of the lowest excited triplet level which is the emitting state of mesitylylene biradical. This requires that the radiative process from the triplet sublevels be faster than the spin-lattice relaxation between the different sublevels. This condition is probably satisfied for the 50-300-ns fluorescence of mesitylylene biradicals.
    No preview · Article · Dec 1987 · The Journal of Physical Chemistry
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    ABSTRACT: The electronic states of the Hg–Ar complex have been studied in a supersonic free jet expansion using a laser double resonance technique. Detailed observations were made of the states correlating with the mercury 6 3P levels 3P0, 3P1, and 3P2. The states correlating with the 3P0 and 3P2 metastable states had not been studied previously since they are optically inaccessible from the ground state. A model was developed which accounts for the structures of the various states. The binding energies can be related simply to the average orientation of the 6p mercury orbital with respect to the internuclear axis. In addition, the Hg(7 3S1)–Ar Rydberg state was reinvestigated and shown conclusively to exhibit a double minimum potential, with a deep well similar to the Hg–Ar+ ion and a shallow van der Waals minimum at larger internuclear distances.
    No preview · Article · Dec 1986 · The Journal of Chemical Physics
  • Y. H. Meyer · O. Benoist D'Azy · M. M. Martin · E. Bréhéret
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    ABSTRACT: The spectral dependence of intensity transients is studied in a multimode pulsed dye laser. It is shown by numerical integration that damping of relaxation oscillations varies as a function of frequency. This new result is discussed in relation to the conceot of spectro-temporal evolution previously introduced and recently applied to short pulse generation.
    No preview · Article · Oct 1986 · Optics Communications
  • T. Montoro · A. Lopez Campillo · B. Soep · O. Benoist D'azy · J.L. Escudero
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    ABSTRACT: Resolved time spectra and decay curves of triptophan in polar solvents have been obtained and examined using the previous results for indol and NMI in the same solvents. Triptophan time resolved fluorescence ant its decay curves were different when the sample was fluid (room temperature) and when it was “glassy” (low temperature). Decay curves depending on frequency were obtained in fluid solutions, meanwhile for “glassy” samples did not appear such dependence. The similar results previously obtained for indole and NMI, were interpreted assuming the reorientation of the solvent dipole moments as a time-depending phenomenum during fluorescence.
    No preview · Article · Mar 1986 · Journal of Molecular Structure
  • O. Benoist^D'azy · F. Lahmani · C. Lardeux · D. Solgadi
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    ABSTRACT: The vibrational and rotational state distributions of the NO X 2Π fragment resulting from photodissociation of cis-CH3ONO excited in specific NO stretching vibrational levels of the neπ* state at 364, 350, 338, 328 and 318 nm have been determined. The NO X ν″ = 0, 1, 2, 3, 4 probed by two-photon laser-induced fluorescence exhibits a large amount of rotational excitation which is independent of the excitation wavelength. The NO X vibrational population varies with the vibrational level prepared in the parent excited molecule and the results show that the excess vibrational energy deposited in the N0 stretching mode of the CH3ONO nπ* state is retained in the vibration of the free NO fragment. The rotational excitation is interpreted in terms of interfragment ccupling due to the impulse applied to the recoiling fragments. The vibrational distribution is more likely to be explained by a simple model based on intrafragment coupling which takes into account the change in N0 bond length between the ground and dissociative state of the molecule.
    No preview · Article · Mar 1985 · Chemical Physics