High resolution vibration-rotation spectrum of the D2O molecule in the region near the 2ν1 + ν2 + ν3 absorption band

The high resolution Fourier transform spectrum of the D₂0 (ν = ν₁ + ν₂/2 + ν₃ = 3.5) polyad was analysed within the framework of the Hamiltonian model taking into account resonance interactions between the seven states (310), (211), (112), (013), (230), (131) and (032). Transitions belonging to the 2ν₁ + ν₂ + ν₃, 3ν₁ +ν₂ and 3ν₂ + 2ν₃ bands were assigned in the experimentally recorded spectrum. This provided the possibility of obtaining spectroscopic parameters of the ‘visible’ states (211), (310) and (032) and of estimating the band centres, and the rotational and resonance interaction parameters of the ‘dark’ states (112) and (131).     

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.     

Shift of the centers of H<Subscript>2</Subscript>O absorption lines in the region of 1.06 μm

The shift coefficients for the lines of the ν₁ + ν₂ + ν₃ and ν₂ + 2ν₃ bands of H₂O in the region from 9403 to 9413 cm^?1 are measured and calculated. The measurements are performed using an intracavity laser spectrometer based on a neodymium laser with a determination error of the line center of 0.003–0.004 cm^?1. The Ar, Kr, and Xe noble gases, as well as nitrogen, oxygen, and hydrogen were used as buffer gases. The coefficients of shifts in eight H₂O absorption lines induced by oxygen, nitrogen, and atmospheric air pressures fall into the region from ?0.004 to ?0.069 cm^?1/bar. The calculations are performed by a semiempirical method using variational wave functions, which, in contrast to other studies, correctly takes into account intramolecular interactions. The calculated values agree satisfactorily with experimental data.     

Low-temperature high-resolution absorption spectrum of 14NH3 in the ν1+ν3 band region (1.51 μm)

Jet-cooled spectra of ¹⁴NH₃ and ¹⁵NH₃ in natural abundance were recorded using cavity ring-down (CRDS, 6584–6670 cm^?1) and cavity enhanced absorption (CEAS, 6530–6700 cm^?1) spectroscopy. Line broadening effects in the CRDS spectrum allowed lines with J ^″-values between 0 and 3 to be identified. Intensity ratios in ¹⁴NH₃ between the jet-cooled CRDS and literature room-temperature data from Sung et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012 K. Sung , L.R. Brown , X. Huang , D.W. Schwenke , T.J. Lee , S.L. Coy , and K.K. Lehmann , J. Quant. Spectrosc. Radiat. Transfer 113 , 1066 (2012).[Crossref], [Web of Science ®] , [Google Scholar]), 1066) further assisted the line assignments. Ground state combination differences were extensively used to support the assignments, providing reliable values for J, K and inversion symmetry of the ground state vibrational levels. CEAS data helped in this respect for the lowest J lines, some of which are saturated in the CRDS spectrum. Further information on a/s doublets arose from the observed spectral structures. Thirty-two transitions of ¹⁴NH₃ were assigned in this way and a limited but significant number (19) of changes in the assignments results, compared to Sung et al. or to Cacciani et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012 P. Cacciani , P. Cermak , J. Cosleou , M. Khelkhal , P. Jeseck , and X. Michaut , J. Quant. Spectrosc. Radiat. Transfer 113 , 1084 (2012).[Crossref], [Web of Science ®] , [Google Scholar]), 1084). Sixteen known and 25 new low-J transitions were identified for ¹⁵NH₃ in the CRDS spectrum but the much scarcer literature information did not allow for any more refined assignment. The present line position measurements improve on literature values published for ¹⁵NH₃ and on some line positions for ¹⁴NH₃.     

Broadening and shift of lines of the ν<Subscript>2</Subscript> + ν<Subscript>3</Subscript> band of water vapor induced by helium pressure

The broadening and shift coefficients of more than 100 absorption lines of the ν₂ + ν₃ band of water vapor that are induced by the pressure of helium are measured and calculated. The broadening and shift coefficients are obtained from analysis of the room-temperature absorption spectra of an H₂O-He mixture measured with a resolution of 0.007 cm^?1 on a Fourier spectrometer in a large range of helium pressures. The specific features in the rotational dependence of the line center shifts are determined, which, in contrast to the broadening induced by other gases, are mainly positive. The calculated coefficients of the line broadening and shift of line centers are determined by a semiclassical method. An unusual dependence of the shift coefficients is explained by the rotational dependence of the intermolecular isotropic interaction potential.     

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     

CO<Subscript>2</Subscript> laser oscillating in the range of 16 μm

The ability of a CO₂ laser to oscillate in the range of 16 (14) μm at room temperature was investigated experimentally and theoretically. The output energy per pulse was ~60 mJ at peak power of ~50 kW. It was necessary to minimize not only harmful losses but also useful ones in both channels 00⁰1–02⁰0 and 02⁰0–0110 and to increase the input energy, i.e., the density of free electrons in the discharge, in order to increase the peak power and energy of 16-μm radiation. The highest values of peak power and energy of radiation were reached at different pressures of the active mixture. The rotational bottleneck effect limiting the peak power and energy of oscillation was important at rather low pressures of the active medium. Oscillation at the R12 line is more preferable than that at the P12 line for use as 9.6-μm dumping radiation.     

Specific heat of the [NH<Subscript>2</Subscript>(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>]<Subscript>2</Subscript>ZnCl<Subscript>4</Subscript> crystal in the temperature region 80–300 K

The specific heat of [NH₂(CH₃)₂]₂ZnCl₄ was measured calorimetrically in the temperature region 80–300 K. As the temperature T decreases, the C _p (T) dependence indicates a phase transition sequence, with the phase transition at T₆=151 K observed for the first time. The thermodynamic characteristics of the crystal were refined. The transformation occurring at T₂=298.3 K is shown to be an incommensurate-commensurate phase transition.     

Saturation-dip measurements in the 2ν<Subscript>2</Subscript> overtone band of OCS with a CO<Subscript>2</Subscript>-laser/microwave-sideband spectrometer

We have employed a CO₂-laser/microwave-sideband spectrometer to carry out saturation-dip sub-Doppler measurements of a number of 2₂ overtone transitions of OCS in the 10-m region. The OCS frequencies have been obtained with an absolute accuracy of order ±37 kHz, as determined from a careful analysis of the combined uncertainties in the frequency of our Lamb-dip-locked laser and the centers of the observed OCS saturation signals. Our ±37 kHz measurement accuracy is consistent with literature OCS sub-Doppler data obtained on a similar instrument. The results serve to extend the comb of precise reference frequencies in the 10-m region and to determine the magnitudes of systematic and random uncertainties of our CO₂ laser. PACS 07.57.Ty; 33.20.Ea; 42.62.Fi     

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.     

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.     

Absorption spectrum of H<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> near 1.06 μm

The absorption spectra of molecular hydrogen plasma excited by electric hollow-cathode and high-frequency discharges are measured. The spectra in the region of 1.06 μm were recorded using a neodymium intracavity laser spectrometer with a resolution of 0.03 cm^?1 and an absorption sensitivity of 10^?8 cm^?1. The absorption lines that can be attributed to the transitions to vibrational states in the molecule are recorded.     

Elastic properties of TeO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Ag<Subscript>2</Subscript>O glasses

A series of glasses [(TeO₂) _x (B₂O₃)_1−x ]_1−y [Ag₂O] _y with x = 70 and y = 10, 15, 20, 25 and 30 mol% were synthesised by rapid quenching. Longitudinal and shear ultrasonic velocity were measured at room temperature and at 5 MHz frequency. Elastic properties, Poisson's ratio, microhardness, softening temperature and Debye temperature have been calculated from the measured density and ultrasonic velocity at room temperature. The experimental results indicate that the elastic constants depend upon the composition of the glasses and the role of the Ag₂O inside the glass network is discussed. Estimated parameters based on Makishima–Mackenzie theory and bond compression model were calculated in order to analyse the experimental elastic moduli. Comparison between the experimental elastic moduli data obtained in the study and the calculated theoretically by the mentioned above models has been discussed.     

Specific features of the magneto-optical properties of α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the IR region

The spectra of reflection and magnetoreflection of light from the crystalline insulator α-Al₂O₃ in the IR spectral region (λ = 2.5–25 μm) are investigated. Some features in the magnetoreflection spectra in the wavelength range corresponding to the excitation of optical phonon modes in α-Al₂O₃ are found. A significant increase in magnetoreflection is observed near these wavelengths. The amplitude and shape of the magnetore-flection spectra for the p and s polarizations of probe light are determined. It is shown that the optical and magneto-optical properties of α-Al₂O₃ in the IR region can be described on the basis of the theory of polaron excitation. A satisfactory correlation between the theoretical and experimental spectra is obtained, which indicates that polarons play an important role in determining the optical characteristics of nonmagnetic insulators and make the dominant contribution to the magnetoreflection spectra.     

Infrared spectra of thin films of α-crystalline hexafluoroethane: a manifestation of resonant dipole–dipole interaction in the range of fundamental vibrational modes ν<Subscript>5</Subscript> and ν<Subscript>10</Subscript>

Infrared reflection-absorption spectra of thin films of α-crystalline hexafluoroethane deposited on a gold-plated copper mirror are measured at temperatures of 70 and 80 K. The bands corresponding to strong in the dipole absorption vibrations ν₅ and ν₁₀ have complex contours, the shape of which is explained in terms of the resonant dipole–dipole interaction between identical spectrally active molecules of the crystal. Splittings of the complex ν5 and ν10 bands are explained taking into account two effects: the Davydov splitting and the LO–TO splitting of the strong modes. Bands of the asymmetric ¹³С¹²СF₆ isotopologue in the absorption spectrum of the crystal exhibit an anomalously large isotope shift as compared with the shift in the spectrum of free molecules. This anomaly is explained by intermolecular resonant dipole–dipole interaction of asymmetric ¹³С¹²СF₆ isotopologue with molecules of the environment, consisting of the most abundant ¹²C₂F₆ isotopologue. The correctness of the given interpretation is confirmed calculating these three effects in the model of resonant dipole–dipole interaction.     

Analysis of the D2O absorption spectrum near 2.5 μm

The D₂O absorption spectrum recorded with a selective modulation Girard spectrometer in the region of 3690–4190 cm⁻¹ (resolution ∼0.07 cm⁻¹) has been analyzed. Based on the fitting of experimental data the spectroscopic parameters of the vibrational state (011) have been determined and the parameters of the vibrational states (110) and (030) have been estimated.     

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.     

Search for ν<Subscript>μ</Subscript> → ν<Subscript>τ</Subscript> oscillations in appearance mode in the OPERA experiment

The OPERA experiment at the underground Gran Sasso Laboratory (LNGS) has to perform the first detection of neutrino oscillations in appearance mode through the direct observation of ν_μ → ν_τ. The apparatus consists of a lead/emulsion-film target complemented by electronic detectors. It is placed in the high-energy, long-baseline CERN neutrino beam (CNGS) 730 km away from the neutrino source. Runs with CNGS neutrinos were successfully carried out in 2008–2009 with the first candidate event ν_μ → gv_τ recently detected.