Water-vapor continuum absorption in the 800–1250 cm−1 spectral region at temperatures from 311 to 363 K

About 200 pure water-vapor spectra covering the region from 800 to 3500 cm^?1 were recorded with resolution of 0.1 cm^?1 at temperatures 311, 318, 325, 339, 352, and 363 K using a 2 m base White cell coupled to the BOMEM DA3.002 FTIR spectrometer. The water-vapor pressure varied from 28 to 151 mbar (21–113 Torr). Under these conditions, the continuum absorbance is quite measurable with the available path lengths up to 116 m. A program was developed for spectral processing that calculates, fits, and removes ro-vibrational structure from the spectrum. The spectra obtained were used to retrieve averaged and smoothed binary absorption coefficients over the region from 800 to 1250 cm^?1. Our continuum data extrapolated to room temperature are in reasonable agreement with the MT_CKD continuum model. But at higher temperatures the MT_CKD model provides very low values, which are up to 50% less than those experimentally measured.     

Infrared spectroscopy of 17O- and 18O-enriched carbon dioxide in the 1700–8300 cm−1 wavenumber region

The assignment of the high resolution Fourier transform spectra of carbon dioxide enriched in ¹⁷O and ¹⁸O which were recorded in LADIR (Paris, France) with the Bruker IFS 125-HR between 1800 and 9000 cm^?1 and in USTC (Hefei, China) with the Bruker IFS 120-HR between 1700 and 9000 cm^?1 was performed. In total 239 bands of 12 isotopologues: ¹⁶O¹²C¹⁶O, ¹⁶O¹²C¹⁸O, ¹⁶O¹³C¹⁶O, ¹⁶O¹³C¹⁸O, ¹⁸O¹²C¹⁸O, ¹⁸O¹³C¹⁸O, ¹⁶O¹²C¹⁷O, ¹⁷O¹²C¹⁷O, ¹⁷O¹²C¹⁸O, ¹⁶O¹³C¹⁷O, ¹⁷O¹³C¹⁷O and ¹⁷O¹³C¹⁸O were observed. Among them, 99 bands were observed for the first time. The majority of new observed bands belong to ¹⁷OCO isotopologues. The positions of 23,003 lines were determined with the experimental uncertainty on the level of 0.001 cm^?1. The spectroscopic constants were fitted to the observed line positions for all observed bands.     

Effective line strengths of trans-nitrous acid near 1275 cm−1 and cis-nitrous acid at 1660 cm−1

We determined the effective line strengths of the trans conformer of nitrous acid (HONO) near 1275 cm^?1 (R-branch of ν₃ mode, NOH bend) and of the cis conformer at 1660 cm^?1 (R-branch of ν₂ mode, NO stretch), both at a spectral resolution of 0.001 cm^?1 by tunable infrared laser differential absorption spectroscopy (TILDAS) utilizing continuous-wave quantum cascade (cw-QC) lasers. Absorbance of one conformer was measured while simultaneously quantifying the mixing ratio of total HONO by catalytic conversion to nitric oxide (NO) followed by calibrated absorption spectroscopy. Line strengths obtained here are consistent with previously reported band strengths for the trans conformer but are lower by a factor of approximately 2.4 for the cis conformer.     

Fourier transform measurements of SO2 absorption cross sections:: I. Temperature dependence in the 24 000–29 000 cm−1 (345–420 nm) region

Absorption cross sections of SO₂ have been obtained in the 24 000–29 000 cm^?1 spectral range (345–420 nm) with a Fourier transform spectrometer at a resolution of 2 cm^?1. Pure SO₂ samples were used and measurements were performed at room temperature (298 K) as well as at 318, 338 and 358 K. This is the first time that temperature effects in this spectral region are reported and investigated. This paper is the first of a series that will report on measurements of the absorption cross section of SO₂ in the UV/visible region at a higher than previously reported resolution and that will investigate temperature effects in support of tropospheric, stratospheric and astrophysical or planetary applications.     

An in situ M?ssbauer study using synchrotron radiation

We have been developing a system for in situ M?ssbauer studies using synchrotron radiation (SR) to elucidate the mechanism of hydrogenation processes. In the system, samples reacts in a pressure-temperature chamber and SR-based M?ssbauer spectra using variable-frequency nuclear monochromator and energy spectra of inelastic nuclear resonant scattering (NRS) of SR are measured. As a feasibility study, the temperature dependence of the M?ssbauer and inelastic NRS spectra of ⁵⁷Fe in c-GdFe₂H₃ under vacuum were measured. In both spectra, clear differences were observed between 373?K and 573?K. These differences can be interpreted by the change of microscopic environment around Fe at the dehydrogenation. Thus, it is confirmed that this system works well enough to perform the in-situ M?ssbauer study on the dehydrogenation of c-GdFe₂H₃.     

Laser infrared spectroscopy of vinyl fluoride in the 1280–1400 cm−1 region

The infrared spectra of CH₂=CHF have been investigated in the ν₅ and ν₆ band regions between 1280 and 1400?cm^?1, at a resolution of about 0.002?cm^?1, using a tunable diode laser spectrometer. These vibrations of symmetry species A′ give rise to a/b-hybrid bands with different contributions from both the components. Spectral analysis resulted in the identification of 1565 (J≤46, K _a ≤11) and 1651 (J≤48, K _a ≤15) transitions of the ν₅ and ν₆ fundamentals, respectively. Both bands are perturbed by the nearby states ν₈?+?ν₉ and ν₉?+?ν₁₁ through different Coriolis resonances and an anharmonic interaction. Using Watson's A-reduction Hamiltonian in the I^r representation and perturbation operators almost all the transitions have been fitted simultaneously to a model including six resonances within the tetrad ν₅/ν₆/ν₈?+?ν₉/ν₉?+?ν₁₁. A set of spectroscopic constants for the ν₅ and ν₆ bands, as well as parameters for the dark states ν₈?+?ν₉ and ν₉?+?ν₁₁ and coupling constants, have been determined. From spectral simulations the dipole moment ratio |Δμ _a /Δμ _b | was estimated to be 0.6?±?0.1 and 2.0±0.3 for the ν₅ and ν₆ bands, respectively.     

An EXAFS study on Bi2Sr2Ca1−xPrxCu2O8−δ single crystal using polarized synchrotron radiation

We have made polarization dependent Extended X-ray Absorption Fine Structure (EXAFS) measurements on a Bi₂Sr₂Ca_1?xPr_xCu₂O_8?δ single crystal in the E//a, E//b and E//a^45° orientations. The results on Cu-K edge and Pr L_III edge EXAFS have been discussed to explain the quenching of superconductivity due to the presence of Pr cation as it was known to destruct the superconductivity by disturbing the local environment around Ca.     

Some improvements of the HNO3 spectroscopic parameters in the spectral region from 600 to 950 cm−1

In an earlier study [Flaud JM, Brizzi G, Carlotti M, Perrin A, Ridolfi M. MIPAS database: validation of HNO₃ line parameters using MIPAS satellite measurements. Atmos Chem Phys 2006;6:1–12] the HNO₃ line parameters in the HITRAN spectroscopic database have recently been revisited in the interval corresponding to the MIPAS spectral range. For the 11.3 μm region these updates involve the line positions for the {ν₅, 2ν₉} bands, and the intensities. However, comparisons between observed spectra recorded by MIPAS and the calculated ones in the 600–950 cm^?1 region still show significant disagreements. The goal of the present paper is to solve some of these problems. Based on the analysis of N₂-broadened HNO₃ laboratory spectra recorded with a Fourier transform instrument, a new HNO₃ database was generated, including the following improvements: (i) approximate parameters for the ν₅+ν₇?ν₇ and ν₅+ν₆?ν₆ hot bands have been added, and (ii) the intensities for the ν₆ and ν₈ bands have been updated. (iii) The air broadening and its temperature dependence, calculated using a semi-classical approach, have been added for each HNO₃ transition. (iv) Finally, line-mixing effects have been pointed out, particularly in the ν₅+ν₉?ν₉ Q branch, and an approach correctly modeling the resulting spectral shape is proposed.     

Radiation-induced sidebands in a Mössbauer spectrum using synchrotron radiation

The resonant interactions of SR with nuclei have been studied in the magnetic dipole approximation. The spontaneous emission spectrum of the nuclei interacting with the SR consists of three types of photons with energiesE-2, E, E + 2, whereE is the energy corresponding to the unperturbed nuclear transition. The relative intensities of the transitions are in the ratios 121. A conventional ME spectrum, the source being an ensemble of SR excited nuclei and a single-line absorber, will display three resonances; the two outer ones are SR-induced sidebands having equal intensity and width.     

The high-resolution infrared spectrum of ethylene in the 1800–2350 cm−1 spectral region

Fourier transform spectra of ethylene (C₂H₄) have been recorded in the 1800–2350?cm^?1 (4.3–5.6?µm) spectral region using a Bruker IFS125HR spectrometer at a resolution of 0.004?cm^?1 leading to the observation of six vibrational bands, ν ₇?+?ν ₈, ν ₄?+?ν ₈, ν ₆?+?ν ₁₀, ν ₆?+?ν ₇, ν ₄?+?ν ₆ and ν ₃?+?ν ₁₀. The corresponding upper state ro-vibrational levels were fit using a Hamiltonian matrix accounting for numerous interactions. A satisfactory fit could be obtained using a polyad of nine interacting states {8¹10¹,?7¹8¹,?4¹8¹,?8¹12¹,?6¹10¹,?6¹7¹,?4¹6¹,?3¹10¹,?3¹7¹} of which three (8¹10¹, 8¹12¹ and 3¹7¹) are unobserved dark states. As a result a much more accurate and extended set of Hamiltonian constants were obtained than previously derived. The following band centers were determined: ν ₀(ν ₇?+?ν ₈)?=?1888.9783(20)?cm^?1, ν ₀(ν ₄?+?ν ₈)?=?1958.2850(20)?cm^?1, ν ₀(ν ₆?+?ν ₁₀)?=?2047.7589(20)?cm^?1, ν ₀(ν ₆?+?ν ₇)?=?2178.011(60)?cm^?1, ν ₀(ν ₄?+?ν ₆)?=?2252.8026(24)?cm^?1 and ν ₀(ν ₃?+?ν ₁₀)?=?2171.2397(20)?cm^?1. Finally, a synthetic spectrum that could be useful for ethylene detection in planetary atmospheres was generated.     

ICLAS of water in the 770 nm transparency window (12 746–13 558 cm−1). Comparison with current experimental and calculated databases

The absorption spectrum of water vapor has been investigated by intracavity laser spectroscopy (ICLAS) in the 12 746–13 558 cm^?1 spectral region corresponding to an interesting transparency window of the atmosphere, partly obscured by the A band of molecular oxygen.The achieved sensitivity—in the order of α_min～10^?9 cm^?1—has allowed one to measure 1062 water lines with intensities ranging from 1.6×10^?28 to 2.35×10^?24 cm/molecule at 296 K. A total of 169 new and improved energy levels belonging to 21 vibrational states could be determined from 374 newly measured transitions. The retrieved experimental line list is compared with the spectra calculated by Schwenke and Partridge, and Barber and Tennyson. Comparison with the available experimental databases shows that the obtained results represent a significant improvement of the knowledge of the water absorption in the considered region, in particular in the region of the oxygen A band.     

CRDS of water vapor at 0.1 Torr between 6886 and 7406 cm−1

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded by high sensitivity CW-Cavity Ring Down Spectroscopy (CW-CRDS) between 6885.79 and 7405.91 cm^?1. This strong absorbing region includes the first hexad of interacting vibrational bands which was previously studied by Fourier Transform Spectroscopy. The achieved sensitivity of the recordings varies from α_min～2×10^–11 to 2×10^?10 cm^?1 allowing us to use a sample pressure of 0.1 Torr, making pressure broadening of the line profile mostly negligible. Weak lines in the vicinity of much stronger lines could then be accurately measured. The weakest lines have intensity on the order of 5×10^–28 cm/molecule at 296 K. A set of 4471 lines were assigned to 4916 transitions of five water isotopologues (H₂ ¹⁶O, H₂ ¹⁸O, H₂ ¹⁷O, HD¹⁶O and HD¹⁸O). A small number of new energy levels was determined mostly for the H₂ ¹⁷O isotopologue. The previous investigations and existing databases are critically evaluated. In particular, a number of corrections and new assignments are proposed for the water list provided by the HITRAN database in the considered region. As a result, a complete list of 12,700 transitions for water in “natural” isotopic abundance is provided as Supplementary Material for the 6885–7408 cm^?1 region.     

Measurements of N2- and O2-broadening and shifting parameters of methane spectral lines in the 5550–6236 cm−1 region

The absorption spectra of mixtures of methane (CH₄) with N₂ and O₂ at different partial pressures of both CH₄ and buffer gases for three temperatures 240, 267, and 296 K have been recorded using the Bruker IFS 125 HR FTIR spectrometer in the 5550–6236 cm^?1 region. The multispectrum fitting procedure has been applied to these spectra to recover the spectral line parameters. The main goal of this procedure was the determination of the N₂- and O₂-broadening and shifting coefficients and the exponents of their temperature dependences. These parameters have been derived for 452 assigned lines with good values of the signal to noise ratio. The rotational dependence of the mean values of these parameters is discussed. The temperature dependence exponents were observed for both N₂ and O₂ buffer gases.     

Absorption spectroscopy of ammonia between 6526 and 6538 cm−1

The spectral measurements of ammonia absorption lines from 6526 to 6538 cm^?1 have been performed at room temperature by using fiber-coupled distributed feedback (DFB) diode laser operating at 1.531 μm. As many as 152 lines of ammonia and its line intensities, self-broadening and air-broadening coefficients were obtained, which include many weak lines not previously reported. The 20 strongest lines were obtained using the traditional direct absorption spectroscopy technology with a 30 cm single-path cell and the other 132 lines were acquired using a compact system based on off-axis integrated-cavity output spectroscopy (OA-ICOS) with an effective optical path of 36.62 m.     

Spectra of carbon disulphide in the 3400–4400 cm−1 region by Fourier transform spectroscopy

Fourier transform spectra have been recorded for carbon disulphide (CS₂) in the region between 3400 cm^?1 and 4400 cm^?1. A data analysis has determined new molecular constants: 14 bands were observed for the main isotopic form ¹²C³²S₂, two bands for the isotopomer ¹²C³²S³⁴S and one each for ¹²C³²S³³S and ¹³C³²S₂.     

Specifics of Heat Transfer in AlxGa1 – xN/GaN Heterostructures on Sapphire

Physics of the Solid State - The thermal conductivity of AlxGa1 – xN/GaN heterostructures (0.05 ≤ x ≤ 1) fabricated on sapphire by molecular beam epitaxy is...