Broadening and collisional interference of lines in the ir spectra of ammonia: Self-broadening in the ν<Subscript>2</Subscript> band

The relaxation parameters of lines of the P, Q, and R branches of the ammonia ν₂ band are calculated in the case of self-broadening with the effects of collisional interference of doublet components taken into account. It is shown that the cross-relaxation parameters do not exceed, as a rule, several percent of the values of the self-broadening coefficients and, consequently, the isolated line approximation is applicable in a wide pressure range. The calculated results are compared with experimental data.     

Broadening and collisional interference of lines in the IR spectra of ammonia: Self-broadening in the ν<Subscript>1</Subscript> band

The relaxation parameters of the lines of the P, Q, and R branches of the ν₁ ammonia ν₁ band are calculated in the case of self-broadening. In the case of doublets, the effects of collisional interference of the doublet components have been taken into account. It is shown that the cross-relaxation parameters of the components can reach ~60% of the values of the self-broadening coefficients, which gives rise to the narrowing of the components and indicates that the isolated line approximation is inapplicable. Comparison with experimental data is made. Good agreement for self-broadening coefficients is obtained. In the case of the self-shift coefficients, discrepancies are considerable in both magnitude and sign, and it is impossible to elucidate their reasons without invoking additional experimental data.     

Measurements of the isotopic composition of UF<Subscript>6</Subscript> according to the fine structure of the IR absorption spectrum in the ν<Subscript>1</Subscript> + ν<Subscript>3</Subscript> band

Absorption spectra of the Q-branch of the ν₁ + ν₃ vibrational–rotational band of uranium hexafluoride (UF₆) recorded in a range of 1290.0–1292.5 cm^–1 using a laser spectrometer based on a quantum cascade laser have been studied. The spectra of samples with a natural isotopic composition (0.7% U²³⁵), an enriched sample (90% U²³⁵), and their gas mixtures (2, 5, and 20% U²³⁵) in a pressure range of 10–70 Torr at a temperature of T = 296 K have been analyzed. The experiments have revealed a highly reproducible fine structure of the recorded spectra. Periodic singularities in the fine-structure spectra have been interpreted as a manifestation of hot band transitions near the Q-branch. Anharmonicity constants X ₂₁, X ₃₁, and X ₃₂ and their combinations X _i1 + X _i3 (i = 4, 5, 6) have been determined. The characteristic features in the fine-structure spectra and the initial spectrum have been used to determine the isotopic composition of enriched UF₆ samples.     

Measurements and calculations of H2-broadening and shift parameters of water vapour transitions of the ν1 + ν2 + ν3 band

The water vapour line broadening and shifting for 97 lines in the ν₁ + ν₂ + ν₃ band induced by hydrogen pressure are measured with Bruker IFS 125 HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm^?1 and in a wide pressure range of H₂. The calculations of the broadening γ and shift δ coefficients were performed in the semi-classical method framework with use of an effective vibrationally depended interaction potential. Two potential parameters were optimised to improve the quality of calculations. Good agreements with measured broadening coefficients were achieved. The comparison of calculated broadening coefficients γ with the previous measurements is discussed. The analytical expressions that reproduce these coefficients for rotational, ν₂, ν₁, and ν₃ vibrational bands are presented.     

The absorption spectrum of D<Subscript>2</Subscript>O in the region of 0.97 μm: the 3ν<Subscript>1</Subscript> + ν<Subscript>3</Subscript> vibrational–rotational band

The vibrational–rotational absorption spectrum of D₂O in the range from 10 120 to 10 450 cm^–1 is recorded on a Fourier transform spectrometer with a resolution of 0.05 cm^–1. The measurements were performed using a multipass White cell with an optical path length of 24 m. A light-emitting diode with brightness higher than that of other devices was used as a radiation source. The signal-to-noise ratio was about 10⁴. The spectrum is interpreted as consisting of lines of more than 400 transitions. The spectral characteristics of lines (centers, intensities, and half widths) are determined by fitting the Voigt profile parameters to experimental data by the least-squares method. The intensities of lines and the experimental rotational energy levels of the (301) vibrational state of the D₂ ¹⁶O molecule with high rotational quantum numbers are determined for the first time.     

Calculation of line parameters of the ν<Subscript>3</Subscript> band of monodeuterated methane: Nitrogen broadening

Halfwidths and shifts of CH₃D lines are calculated for the case of nitrogen broadening. The calculations are performed for room temperature (296 K) for vibrational–rotational lines in the ν₃ parallel band, with the rotational quantum numbers varying in the ranges of 0 ≤ J ≤ 70 and 0 ≤ K ≤ 20. For each line, the temperature-dependence characteristics are calculated in the range of 200–400 K recommended for the HITRAN database. The calculations are carried out using a semiempirical method with a correction factor the parameters of which are adjusted on a number of experimental values.     

Line mixing in the water vapour transitions of the ν1 + ν2 + ν3 band perturbed by helium pressure

The line mixing effect for two pairs of transitions with rotational quantum numbers (3 1 2)?←?(4 1 3), (3 2 1)?←?(4 2 2), (4 3 1)?←?(3 3 0) and (4 2 2)?←?(3 2 1) in the ν₁?+?ν₂?+?ν₃ band of H₂O has been studied. The measurements were performed at room temperature, at the spectral resolution of 0.01?cm^?1 and in a wide pressure range of helium. Pressure-broadening and -shifting coefficients and mixing parameter were obtained with help of the line profile using the Rosenkranz first-order approximation.     

On the accurate determination of pressure- induced line shifts in the 2ν<Subscript>3</Subscript> band of H<Subscript>2</Subscript>O at 1320 nm

A simple technique is demonstrated for the accurate determination of pressure-induced line shifts of water in air. High- and low-pressure water samples are simultaneously probed on selected overtone transitions at 1.32 μm using a current-modulated distributed-feedback diode laser and harmonic detection. The resultant profiles yield an average line shift of -293±30 MHz/atm for the 3,3,0 (002)2,2,1 (000)transition at 227251 GHz and -134±7 MHz/atm for the 3,2,1 (002)2,1,2 (000) transition at 227027 GHz. Comparisons are made between first- and second-harmonic detection, and wavelength- and frequency-modulation regimes. The effect of modulation broadening on the returned line shifts is quantified. Received: 12 August 2002 / Revised version: 21 October 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +44-01865/275410, E-mail: gus.hancock@chemistry.ox.ac.uk     

Influence of Matrix Nature on the Structural Characteristics of In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CeO<Subscript>2</Subscript> and SnO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> Composites Fabricated by the Impregnation Method

The structural characteristics, valence states, and distribution of cerium ions between the components in In₂O₃–CeO₂ and SnO₂–CeO₂ nanocomposites fabricated using the impregnation method were studied. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) were used to show that, during impregnation, cerium ions are not included into In₂O₃ crystals and are disposed only on their surface in the form of nano-sized crystallites or amorphous clusters. On the other side, under the contact of CeO₂ clusters with a surface of SnO₂ matrix crystals, cerium ions penetrate into the surface layer of these crystals. In contrast to an In₂O₃–CeO₂ system, where the addition of CeO₂ does not affect the conduction activation energy, where cerium oxide is added to SnO₂, the observed increase in the resistance of a SnO₂–CeO₂ composite is accompanied by a sufficient increase in activation energy. These data and the XPS spectra confirm the modification of the surface layers of conductive SnO₂ crystals as, a result of the penetration of cerium ions into these layers.     

Temperature dependence of the quenching of N<Subscript>2</Subscript> (C <Superscript>3</Superscript>Π<Subscript>u</Subscript>) by N<Subscript>2</Subscript> (X) and O<Subscript>2</Subscript> (X)

The temperature dependences of the quenching rate constants of the states N₂ (${\rm C} \ {^{3}{ \rm \Pi }_{u}}${\rm C} \ {^{3}{ \rm \Pi }_{u}} v^′=0,1) by N₂ (X) and of the state N₂ (${\rm C} \ {^{3}{ \rm \Pi }_{u}} \ v^{\prime}=0${\rm C} \ {^{3}{ \rm \Pi }_{u}} \ v^{\prime}=0) by O₂ (X) are studied. Time-resolved light emission from the gas was analyzed in the temperature range from 300 K to 210 K keeping the gas at constant density. In case of quenching by N₂ (X), the quenching rate constant for the vibrational level v^′= 0 increases by (13 ±3)% with gas cooling whereas the quenching rate constant for v^′= 1 decreases by (5.0 ±2.5)% in this temperature range. For quenching by O₂ (X), the quenching rate constant decreases by (3 ±2)% with gas cooling. The temperature variation of the N₂ (C ³Π_u v^′=0) emission intensity for pure nitrogen and dry air are calculated using the obtained quenching rate constants and is compared with the experimental data available in the literature.     

Study of the KNO<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system by differential scanning calorimetry

The structural and the thermodynamic properties of potassium nitrate KNO₃ and its composites with nanosized aluminum oxide Al₂O₃ have been studied by differential scanning calorimetry. It has been found that an amorphous phase forms in composites (1–x)KNO_3–xAl₂O₃. The thermal effect corresponding to this phase has been observed at 316°C. It has been found that the phase transition heats of potassium nitrate decreased as the aluminum oxide fraction increased.     

Fabrication of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> bi-functional composites with hierarchical and hollow structures and their application in water treatment

The α-Fe₂O₃/TiO₂ bi-functional composites with hierarchical and hollow structures are fabricated through a hydrothermal route. The adsorption performance and photocatalytic activity of the composites towards Pb²⁺ are investigated in this work. Different adsorption kinetics models and equilibrium models are used to explore the adsorption behavior of hierarchical α-Fe₂O₃/TiO₂ hollow spheres. Experimental data show that adsorption kinetics of the hierarchical α-Fe₂O₃/TiO₂ hollow spheres can be fitted well by the pseudo-second-order model, while the isothermal data can be perfectly described by the Langmuir adsorption model. The maximum adsorption capacity of the hierarchical α-Fe₂O₃/TiO₂ hollow spheres is 32.36 mg g^?1. Moreover, the hierarchical α-Fe₂O₃/TiO₂ hollow spheres possess photocatalytic oxidation character under simulated solar light irradiation. The results demonstrate that the hierarchical α-Fe₂O₃/TiO₂ hollow spheres, as effective and cheap materials, can be applied to the removal of heavy metal ions from wastewater.