J. Deson

Vacuum UV photolysis of CO2. Rare-gas oxide formation in matrices

Abstract In this paper, we report experimental results obtained upon photolysis of CO 2 trapped at low concentrations (0.1%) in neon, argon and krypton matrices. The mixture are photolysed using a xenon resonance lamp emitting photons at 8.4 eV. Only in a neon matrix does the photolysis of CO 2 lead to O( 1 D) → O( 3 P) emission. Furthermore, oxygen atoms are shown to diffuse at all temperatures in a neon matrix (as detected by molecular oxygen emission), whereas in the other matrices this occurs only when the sample is warmed even though irradiation is performed at high temperature. In argon and krypton matrices, O( 1 S) → O( 1 D) emission is observed even though there is not enough energy to form an O( 1 S) atom in a primary photodecomposition process. This suggests that O( 1 D) becomes bound to argon or krypton atoms as a stable rare-gas oxide RGO excimer, which is subsequently excited and photolysed by 8.4 eV photons. These observed features are explained using a model for the interaction between oxygen ( 3 P, 1 D, 1 S) and rare-gas atoms ( 1 S) which had previously been proposed to account for the emission spectra of oxygen atoms observed during photolysis of oxygenated compounds.

Emission spectra and radiative lifetimes of the Cameron bands of CO trapped in solid rare gas matrices

The emission spectrum of the Cameron bands (a 3Π→X1 Σ+) of CO molecules trapped in solid Ne, Ar, and Kr has been studied using Xe resonance lamp excitation (λ=147 nm). The lifetime of the a 3Π state has been measured in solid Ne and found to be 90 msec. The decay time of this state is exponential within the range of experimental errors. The lifetime has been calculated assuming spin–orbit mixing between 1Σ+ and 3Π0 states, and found to be 94 msec for J=0. The lifetime values in Ar and Kr matrices are found to be 7.2 and <1 msec, respectively; this is consistent with the matrix shifts in solid Ne, Ar, and Kr, which for the 0–0 bands have been found to be −305, −946, and −2812 cm−1, respectively.

laser-induced luminescence in reduced copper-exchanged Y zeolite

Abstract Copper-exchanged sodium Y zeolite exhibit broad-band emission under 240 nm laser photoexcitation. A kinetic study of the decay of the luminescence spectrum reveals three components with contributions which depend on the thermal pretreatment of the sample, dehydration or reduction in hydrogen. Identification of two of the emitting centres as Cu + sites indicates that autoreduction accompanies dehydration. Prolonged reduction in hydrogen diminishes the concentration of these species.

Characterization of Cu+ ions in CuHZSM-5 zeolites and CuSAPO-34 molecular sieve Cu+ laser-induced luminescence and 129Xe-NMR diagnosis

Abstract We report on an attempt to characterize by laser-induced phosphorescence spectroscopy Cu+ sites at low concentration in CuHZSM-5 and CuSAPO-34 samples which have been heated to 623 K in vacuum. Evidence is given that atleast two different sites for the copper ion location are available in the ZSM-5 structure. The laser-induced luminescence diagnosis of Cu+ ions allows a determination of the relative concentration of these sites in the samples. It provides evidence that the concentration of sites with square pyramidal symmetry varies linearly with the total number of Cu+ ions per unit cell. The signal intensity of Cu+ is highly dependent on the site environment and especially on the Al position. 129Xe-NMR confirms the presence of Cu+ and that there is no Cu2+ interacting with Xe in the zeolite pores.

Matrix-isolation study of the co2 lowest triplet state

Abstract We have investigated the emission of a CO 2 molecule isolated in an Ar matrix at 4.7 K in the spectral region between 350 and 550 nm. This emission is a continuum with a lifetime of 570 ms. We assign it to the transition from the lowest triplet state (bent) 3 B 2 to the fundamental state (linear) 1 Σ + g .

LASER-INDUCED FLUORESCENCE OF QUINOLINE ADSORBED ON ACIDIC ZEOLITES

Abstract Laser-induced fluorescence spectra of quinoline adsorbed on different forms of acidic Y zeolite reveal interactions between the adsorbate and different polarizing sites in the supercages. Bronsted acid sites protonate quinoline whereas Lewis acid sites appear to give a charge-transfer complex whose fluorescence is strongly red-shifted compared to that of the quinolinium ion. An unstable hydrogen-bonded complex is formed with non-acidic silanol groups.

Bicolor laser photoexcitation of NO in SF6 sensitized system

Abstract The fluorescence from NO vibronic states exhibited when a pulsed UV laser irradiation is combined with a cw IR laser excitation, has been investigated in an energy range close to the dissociation threshold. The observed formation of the NO D2Σ+ (ν′= 0) Rydberg state in high rotational levels requires the absorption of one UV quantum at λ = 193.3 nm by molecules of NO which previously had an internal energy equivalent to four CO2 laser quanta. Moreover the UV laser beam is used to probe the temperature of the sample pumped by the cw CO2 laser. The population of NO B 2Π(ν′ = 7) valence state is strongly enhanced under bicolor irradiation compared to what occurs with single UV irradiation. From a Boltzmann rotational energy distribution, a temperature of 450 K has been determined in the reactional zone.

Obtention des bandes de cameron par photo excitation de co en matrices d'argon de krypton et de xenon

Abstract CO trapped in solid matrices of argon, krypton and xenon has been excited by 10 eV photons. Cameron bands v ′=0, v ″=0,1,2,3,4 are observed during the irradiation. If red shifts are observed in argon and krypton matrices, the transition in xenon shows no differences with gas phase data.

ANALYSIS OF ACIDIC SITES IN NAFION-H AND NAFION-H/SILICA GEL NANOCOMPOSITES BY LASER-INDUCED FLUORESCENCE SPECTRA OF QUINOLINE ADSORBED ON THE SURFACE

Abstract Laser-induced fluorescence spectroscopy of quinoline adsorbed on the surface of Nafion-H and Nafion-H/silica gel nanocomposites is used to characterize the acidic sites.

Laser-Induced Fluorescence of Base Adsorbed on Surface Sites in Solid Catalysts

The interaction of quinoline with the surface of Nafion-H and Nafion-H (13 wt%)/silica gel composites, silica gel itself, HY zeolite, dealuminated or not, and two types of alumina is studied by laser-induced fluorescence. Strong Brønsted acid sites interact with quinoline to form the quinolinum, that ion being revealed by a band peaking at 390 nm. When Lewis acid sites are present, a complex formed between these sites and quinoline is observed. A dimeric species and the diffusion of the adsorbates on the surface of the Nafion-H polymer are discussed.