Multi-photon and electron impact ionisation studies of reactivity in adenine–water clusters

Multi-photon ionisation (MPI) and electron impact ionisation (EII) mass spectrometry experiments have been carried out to probe unimolecular and intermolecular reactivities in hydrated adenine clusters. The effects of clustering with water on fragment ion production from adenine have been studied for the first time. While the observation of NH4+ fragments indicated the dissociation of protonated adenine, the dominant hydration effects were enhanced C4H4N4+ production and the suppression of dissociative ionisation pathways with high activation energies. These observations can be attributed to energy removal from the excited adenine radical cation via cluster dissociation. Comparisons of MPI and EII measurements provided the first experimental evidence supporting hypoxanthine formation in adenine–water clusters via theoretically predicted barrierless deamination reactions in closed shell complexes

On a multi-threshold compound Poisson process perturbed by diffusion

We consider a multi-layer compound Poisson surplus process perturbed by diffusion and examine the behaviour of the Gerber-Shiu discounted penalty function. We derive the general solution to a certain second order integro-differential equation. This permits us to provide explicit expressions for the Gerber-Shiu function depending on the current surplus level. The advantage of our proposed approach is that if the diffusion term converges to zero, the above-mentioned explicit expressions converge to those under the classical compound Poisson model, provided that the same initial conditions apply. This is subsequently illustrated by an extended example related to the probability of ultimate ruin.

Optical properties of gas-phase tryptophan-silver cations : charge transfer from the indole ring to the silver atom

International audienceWe present a joint experimental and theoretical investigation of the electronic excitation spectra of the tryptophan-silver complex. The photodissociation spectrum of gas-phase [Trp-Ag]+ was measured from 215 to 330 nm using a quadrupole ion trap coupled to an optical parametric-oscillator laser. The calculated time-dependent density functional theory (TD-DFT) absorption spectra for different prototypes of structures are presented. Low-energy transitions that are experimentally observed are only calculated for the charge-solvation (CS) structures. These transitions are a signature of the metal- interaction in [Trp-Ag]+. The recorded spectrum is compared to a Boltzmann average of the absorption spectrum obtained from direct molecular dynamics (MD) simulations involving simultaneous transitions to excited states based on semiempirical configuration interaction (CI) calculations. The results demonstrate that charge transfer can be photoinduced from the indole ring to the silver atom

NANOSTRUCTURED ZrO2 POWDER SYNTHESIZED BY ULTRASONIC SPRAY PYROLYSIS

The synthesis of nanostructured zirconia particles from aqueous colloidal dispersion of zirconia (zirconia sol) was carried out by ultrasonic spray pyrolysis method. The morphology of these nanostructured particles was characterized by scanning electron microscopy and transmission electron microscopy. The synthesized particles are spherical in shape with the avarage size of 400 nm, consisting of smaller primary particles, with the mean crystallite size of 7 nm. The tetragonal phase was confirmed by both X-ray and electron diffraction measurements.Ultrasonic spray pyrolysis, nanostructured zirconia particles, zirconia sol

Spectroscopy of isolated, mass-selected tryptophan-Ag3 complexes : A model for photoabsorption enhancement in nanoparticle-biomolecule hybrid systems

International audienceWe wish to show that gas-phase studies of small metal cluster-biomolecule complexes provide fundamental insights into the mechanism leading to enhanced optical absorption in nanoparticle-biomolecular hybrid systems. Here we present, for the first time, a joint experimental and theoretical study of photoabsorption and photofragmentation of the silver trimer-tryptophan cation complex ([Trp·Ag3]+). We demonstrate that binding the metal cluster to a biomolecule leads to a remarkably high optical absorption as compared to the bare tryptophan or the [Trp·Ag]+ complex. As calculations show this arises due to coupling between the excitations in the metallic subunit with a charge transfer excitation to the tryptophan molecule

Orange-Reddish Light Emitting Phosphor GdVO4:Sm3+ Prepared by Solution Combustion Synthesis

The gadolinium vanadate doped with samarium (GdVO4:Sm3+) nanopowder was prepared by the solution combustion synthesis (SCS) method. After synthesis, in order to achieve the full crystallinity, the material was annealed in air atmosphere at 900°C. Phase identification in the postannealed powder samples was performed by X-ray diffraction, and morphology was investigated by high-resolution scanning electron microscopy (SEM). Photoluminescence characterization of the emission spectrum and time-resolved analysis have been performed using the tunable laser optical parametric oscillator excitation and the streak camera. Several strong emission bands in the Sm3+ emission spectrum were observed, located at 567 nm (4G5/2–6H5/2), 604 nm (4G5/2–6H7/2), and 646 (654) nm (4G5/2–6H9/2), respectively. The weak emission bands at 533 nm (4F3/2–6H5/2) and 706 nm (4G5/2–6H11/2) and a weak broad luminescence emission band of VO43− were also observed by the detection system. We analyzed the possibility of using the host luminescence for two-color temperature sensing. The proposed method is improved by introducing the temporal dependence in the line intensity ratio measurements