Photocatalytic Activity in CH

Some TiO2 powders, prepared from titanium(IV)tetraisopropoxide by the sol-gel method and thermally treated between 100 and 1000∘C, have been characterized by X-ray powder diffraction and by nitrogen adsorption and desorption at 77 K to calculate the BET-specific surface area, from which the micropore volume and the external surface area can be derived. The photocatalytic activity (ka) of the above powders has been evaluated considering the TiO2-sensitized photo-oxidation of 4-methoxybenzyl alcohol in CH3CN as the test reaction. The decrease of ka have been related to the decrease of the BET surface area, the micropore volume, and the external surface area of the TiO2 powders, but a satisfactory linear correlation is observed only for the last superficial parameter

A Molecular Beam Scattering Study of the Weakly Bound Complexes of Water and Hydrogen Sulphide with the Main Components of Air

International audienceTotal integral cross section experiments, for collisions of rotationally hot water and hydrogen sulphide projectiles by O2 and N2 targets, are reported for the first time. The experimental data allowed the determination of effective potential energy curves which are representative of the intermolecular interactions averaged over all possible relative configurations of these weakly bound complexes. Such information is relevant for the modelling of elementary processes occurring in planetary atmospheres. These experimental determinations have been also used to test the accuracy of intermolecular interactions provided by ab initio calculations, recently available for the water containing complexes. We further investigated possible experimental effects due to interaction components other than the van der Waals one and some evidences have been found for the complexes of water while these effects appear to be below the experimental sensitivity for the hydrogen sulphide containing complexes

Mass spectrometric study of double photoionization of HBr molecules

The double photoionization of HBr molecules, by synchrotron radiation in the energy range between 25 and 55 eV, has been studied in a mass spectrometric experiment. The HBr21 and Br21 product ions have been detected by a photoelectron-photoion-coincidence technique, while the H11Br1 formation, which follows the double ionization of HBr, has been studied by photoelectron-photoion-photoion-coincidence technique. HBr21 ions are produced with a threshold of 32.460.4 eV, while the dissociative channel leading to H11Br1, shows a threshold around 33 eV. The production of H1Br21 occurs with a threshold of 40.260.4 eV. These results appear to be in a fairly good agreement with earlier nonrelativistic calculations of potential energy curves and also with values indirectly obtained from experimental Auger spectra

Determination of Structural Parameters from Advanced Molecular Electronic Spectroscopy: The Double Ionization of Nitrous Oxide by Synchrotron Radiation

The double photoionization of N2O molecules, in the 30–50 eV energy range, has been studied by synchrotron radiation. In the whole energy range, dissociative ionization producing N+ + NO+ or N+ 2 + O+ has beenobserved. These two processes appear to occur also below the vertical threshold of 35.8 eV, where the double ionization should be indirect. In the range between 35.8 and 38.5 eV. The two processes occur instead by direct coulomb explosion of the N2O2+ dication. Above 38.5 eV, the dissociation leading to NO+ + N+ is also promoted by the formation of a dication metastable state, which decays by fluorescence to the ground state and then dissociates

Dissociative double photoionization of singly deuterated benzene molecules in the 26-33 eV energy range

This work provides new experimental and theoretical results about the formation and dissociation of benzene dication. The experiment has been carried out by using a vacuum ultraviolet radiation from a synchrotron source together with a time-of-flight spectrometer and a position sensitive ion detector. Isotopically labeled benzene molecules with a single deuterium atom have been used in order to study the symmetric dissociation of the benzene dication, not well evident in previous experiments. A threshold of 30.1 ± 0.1 eV has been observed for this dissociation reaction. Moreover, the lifetime of the dissociation of the benzene metastable dication producing CH3 + and C5H3 + has been obtained as a function of the photon energy, by the use of a Monte Carlo trajectory analysis of the coincidence distributions. The determined lifetime is independent of the photon energy and has an average value of 0.75 ± 0.22 μs. Theoretical calculations of the energy and structure of dissociation product ions have been also performed to provide crucial information about the dynamics of the charge separation reactions following the photoionization event

Threshold-photoelectron-spectroscopy-coincidence study of the double photoionization of HBr

A threshold-photoelectron-coincidence spectrum of HBr has been recorded in the 32.2–35.8 eV photon energy range, with a resolution of ;0.01 eV, using a synchrotron radiation source. The X 3S2 and a 1D2 states of the HBr21 dication are clearly observed in the spectrum, while there is no clear evidence for the formation of the b 1S1 electronic state. For the first two states, the vibrational states v50 – 3 have been resolved, while for the ground X 3S2 state also spin–orbit splitting has been detected. The results appear in good agreement with previous experimental observations. A comparison with theoretical predictions indicates the role of ‘‘noncovalent’’ contributions to the interaction between the two atomic partners for the formation of metastable states

Physical Chemistry Chemical Physics

p. 8245-8260This work provides new experimental and theoretical results about the formation and dissociation of benzene dication. The experiment has been carried out by using a vacuum ultraviolet radiation from a synchrotron source together with a time-of-flight spectrometer and a position sensitive ion detector. Isotopically labeled benzene molecules with a single deuterium atom have been used in order to study the symmetric dissociation of the benzene dication, not well evident in previous experiments. A threshold of 30.1 ± 0.1 eV has been observed for this dissociation reaction. Moreover, the lifetime of the dissociation of the benzene metastable dication producing CH3+ and C5H3+ has been obtained as a function of the photon energy, by the use of a Monte Carlo trajectory analysis of the coincidence distributions. The determined lifetime is independent of the photon energy and has an average value of 0.75 ± 0.22 μs. Theoretical calculations of the energy and structure of dissociation product ions have been also performed to provide crucial information about the dynamics of the charge separation reactions following the photoionization event