FTIR measurements of CO2 line positions and intensities at high temperature in the 3700-3750 cm spectral region

Positions and intensities for 453 spectral lines in 12 rovibrational bands of ¹²C¹⁶O₂ have been determined between 3700 and 3750 cm⁻¹. At three temperatures (294, 500, and 698 K) eight spectra have been recorded at a pressure around 5 mbar and for an absorption path of about 190 cm⁻¹ using a Bomen DA3 Fourier transform spectrometer (4 × 10⁻³ cm⁻¹ resolution). Some of the measured positions and intensities can be compared with recent experimental results that validate the experimental set-up and the data analysis procedure. The results are also compared with the values listed in the HITRAN 2000 database. If the agreement is generally good, discrepancies are observed for three hot bands.     

Infrared absorption cross sections for ethane (C2H6) in the 3 μm region

Infrared absorption cross sections for ethane have been measured in the 3 μm spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125/HR). Results are presented for pure ethane gas from spectra recorded at 0.004 cm⁻¹ resolution and for mixtures with dry synthetic air from spectra obtained at 0.015 cm⁻¹ resolution (calculated as 0.9/MOPD using the Bruker definition of resolution), at a number of temperatures and pressures appropriate for atmospheric conditions. Intensities were calibrated using three ethane spectra (recorded at 278, 293, and 323 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database.     

Infrared absorption cross-sections for acetaldehyde (CH3CHO) in the 3 μm region

A series of infrared absorption cross-sections for acetaldehyde has been measured in the 3 μm region from spectra obtained using a high-resolution Fourier transform spectrometer (Bruker IFS 125/HR). Results presented are for mixtures of acetaldehyde vapor combined with pure synthetic air taken at various temperatures and pressure to simulate atmospheric conditions found principally in the Earth's troposphere and lower stratosphere. Spectra were recorded at a resolution of 0.005 cm⁻¹ and intensities were calibrated using three acetaldehyde spectra (measured at 278, 298 and 323 K) provided by the Pacific Northwest National Laboratory (PNNL) IR database.     

Terahertz absorption spectra of nitromethane

Nitromethane, with its heavy frame and internal rotator, readily evaporates into the atmosphere making it an ideal candidate for remote sensing. Here we present the absorption spectra of gas-phase nitromethane between 9 and 50 cm⁻¹. Measurements were taken using a Bruker IFS 66v Fourier transform far-infrared (FTIR) spectrometer at a resolution of 0.12 cm⁻¹ (0.0036 THz) from 9 to 40 cm⁻¹ and a Bruker Vertex 80v FTIR spectrometer with a resolution of 0.0075 cm⁻¹ (0.00226 THz) from 10 to 50 cm⁻¹. The absorption spectra were measured at multiple pathlengths ranging from 2 to 6 m. These measurements were used to calculate the absorption coefficient of nitromethane as a function of wavenumber.     

The application of Raman and anti-stokes Raman spectroscopy for in situ monitoring of structural changes in laser irradiated titanium dioxide materials

The use of Raman and anti-stokes Raman spectroscopy to investigate the effect of exposure to high power laser radiation on the crystalline phases of TiO₂ has been investigated. Measurement of the changes, over several time integrals, in the Raman and anti-stokes Raman of TiO₂ spectra with exposure to laser radiation is reported. Raman and anti-stokes Raman provide detail on both the structure and the kinetic process of changes in crystalline phases in the titania material. The effect of laser exposure resulted in the generation of increasing amounts of the rutile crystalline phase from the anatase crystalline phase during exposure. The Raman spectra displayed bands at 144 cm⁻¹ (A1g), 197 cm⁻¹ (Eg), 398 cm⁻¹ (B1g), 515 cm⁻¹ (A1g), and 640 cm⁻¹ (Eg) assigned to anatase which were replaced by bands at 143 cm⁻¹ (B1g), 235 cm⁻¹ (2 phonon process), 448 cm⁻¹ (Eg) and 612 cm⁻¹ (A1g) which were assigned to rutile. This indicated that laser irradiation of TiO₂ changes the crystalline phase from anatase to rutile. Raman and anti-stokes Raman are highly sensitive to the crystalline forms of TiO₂ and allow characterisation of the effect of laser irradiation upon TiO₂. This technique would also be applicable as an in situ method for monitoring changes during the laser irradiation process.     

Infrared absorption cross sections for propane (C3H8) in the 3 μm region

Infrared absorption cross sections for propane have been measured in the 3 μm spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125 HR). The spectra of mixtures of propane with dry synthetic air were recorded at 0.015 cm⁻¹ resolution (calculated as 0.9/MOPD using the Bruker definition of resolution), at a number of temperatures and pressures appropriate for atmospheric conditions. Intensities were calibrated using two propane spectra (recorded at 278 and 293 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database.     

Intensities and self-broadening coefficients of the CO2 Ro-vibrational transitions measured by a near-IR diode laser spectrometer

Eleven absorption lines belonging to one of the Fermi-tetrad bands of CO₂, (3, 0⁰, 1)_III centered at 6231 cm⁻¹, have been recorded by a newly constructed near-infrared diode laser spectrometer. Precise line parameters, linestrength, and self-broadening parameters were determined from the observed spectra by analyzing the data using the Galatry profile function.     

Near infrared spectroscopy of carbon dioxide. II: OCO and OCO line positions

High-resolution near-infrared (4000-8500 cm⁻¹) spectra of ¹³C-enriched carbon dioxide have been recorded using the McMath-Pierce Fourier transform spectrometer at the Kitt Peak National Solar Observatory. We observed over 1000 line positions for the ¹⁶O¹³C¹⁶O isotopologue, the majority of which have previously been observed only in spectra of the Venusian atmosphere [J. Mol. Spectrosc. 67 (1977) 304]. These have been analyzed to determine spectroscopic constants for 28 different vibrational states. The analysis yielded RMS fitting residuals <1.5 × 10⁻⁴ cm⁻¹ for the strongest bands and RMS residuals <5 × 10⁻⁴ cm⁻¹ for most other fitted bands. A 5% ¹⁸O-enrichment in the sample enabled us to observe 410 line positions from 5 near-infrared vibrational bands of the ¹⁶O¹³C¹⁸O isotopologue. Analysis of the ¹⁶O¹³C¹⁸O bands yielded RMS fitting residuals <2 × 10⁻⁴ cm⁻¹. Additionally, the first fits for the ¹⁶O¹³C¹⁸O 11101 ← 01101 and 11102 ← 01101 hot bands yielded RMS residuals of 2.3 × 10⁻⁴ and 2.2 × 10⁻⁴ cm⁻¹, respectively. Critical reevaluations of the spectroscopic constants for the low lying vibrational states for both isotopologues have been performed as part of the analysis.     

Global modeling of CO2 absolute line intensities from CW-CRDS and FTS measurements in the 1.6 and 2.0 μm regions

Line intensities of ¹³C¹⁶O₂ have been measured between 5851 and 6580 cm⁻¹ using CW-cavity ring down spectroscopy (CRDS) and in the 4700-5050 and 6050-6850 cm⁻¹ regions using Fourier transform spectroscopy. As a result of the high sensitivity (noise equivalent absorption α_min∼3×10⁻¹⁰ cm⁻¹) and high dynamics allowed by CW-CRDS, accurate line intensities of 2039 transitions ranging between 1.1×10⁻²⁸ and 1.3×10⁻²³ cm⁻¹/(molecule cm⁻²) were measured with an average accuracy of 4%. These transitions belong to a total of 48 bands corresponding to the ΔP=9 series of transitions. Additionally, unapodized absorption spectra of ¹³C-enriched samples have been recorded using a high-resolution Bruker IFS125HR Fourier transform spectrometer. Spectral resolutions of 0.004 cm⁻¹ (maximum optical path difference (MOPD)=225 cm) and 0.007 cm⁻¹ (MOPD=128.6 cm), and pressure×path length products in the ranges 5.2-12 and 69-450 hPa×m have been used for the lower and higher energy spectral regions, respectively. Absolute line intensities have been measured in the 2001i−00001, 3001i−00001 (i=1, 2, 3) and 00031−00001 bands. An excellent agreement was achieved for the line intensities of the 3001i−00001 (i=1, 2, 3) bands measured by both FTS and CW-CRDS. The CW-CRDS and FTS experimental intensity data together with selected intensity information from the literature have been fitted simultaneously using the effective operators approach. Two sets of effective dipole moment parameters have thus been obtained, which reproduce the observed line intensities in the 2.0 and 1.6 μm regions within experimental uncertainties.     

High sensitivity cw-cavity ringdown and Fourier transform absorption spectroscopies of CO2

The absorption spectrum of ¹³CO₂ has been recorded by cw-cavity ringdown spectroscopy with a new set up based on fibered DFB lasers. By using a series of 31 DFB lasers, the spectrum of carbon dioxide could be recorded in the 6130-6750 cm⁻¹ region with a typical sensitivity of 5 × 10⁻¹⁰ cm⁻¹. The spectrum has also been recorded between 4400 and 8500 cm⁻¹ with a Fourier transform spectrometer associated with a multi-pass cell (maximum path length of 105 m). The new observations obtained both by FTS and CRDS represent a significant extension of the available data. For instance, more than 4000 line positions were measured and assigned in the CRDS spectrum while only 232 line positions are listed in the HITRAN database. Altogether, the band by band analysis has led to the determination of the rovibrational parameters of 65, 7, and 24 bands for the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁷O, and ¹⁶O¹³C¹⁸O isotopomers, respectively. As some observed line positions show significant deviations from the predictions of the effective Hamiltonian model, the new observed line positions were gathered with the data available in the literature to refine the set of effective Hamiltonian parameters of the ¹³C¹⁶O₂ isotopic species. The refined set of 96 effective Hamiltonian parameters reproduces more than 14 650 line positions of ¹³C¹⁶O₂ with an RMS=0.002 cm⁻¹. A detailed comparison with the line positions retrieved from Venus spectra and the line list provided by HITRAN is also presented and discussed.     

Lorentz half-width, pressure-induced shift and speed-dependent coefficients in oxygen-broadened CO2 bands at 6227 and 6348 cm using a constrained multispectrum analysis

The McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory (NSO) on Kitt Peak, Arizona, was used to record infrared high resolution absorption spectra of CO₂ spectra broadened by O₂. These spectra were analyzed to measure O₂-broadened half-width coefficients, O₂-induced pressure-shift coefficients and speed dependent parameters for transitions in the 30013←00001 and 30012←00001 bands of ¹⁶O¹²C¹⁶O located near 6227 and 6348 cm⁻¹, respectively. All spectra were obtained at room temperature using the long path, 6 m base path White cell available at NSO. A multispectrum nonlinear least-squares fitting algorithm employing Voigt line shapes modified to include line mixing and speed dependence was used to fit simultaneously a total of 19 spectra in the 6120-6280 cm⁻¹ (30013←00001) and 6280-6395 cm⁻¹ (30012←00001) spectral regions. 16 of the 19 spectra analyzed in this work were self broadened and three spectra were lean mixtures of CO₂ in O₂. The volume mixing ratios of CO₂ in the three spectra varied between 0.06 and 0.1. Lorentz half-width and pressure-induced shift coefficients were measured for all transitions in the P(50)-R(50) range in both vibrational bands. The results obtained from present analysis have been compared with measurements available in the literature for self-, air-, oxygen- and argon-broadening. No significant differences were observed between the broadening and shift coefficients of the two bands. The N₂-broadened half-width and pressure-shift coefficients were computed from measured air- and O₂-broadened width and shift coefficients.     

Fourier-transform infrared emission spectroscopy of BO

The Fourier-transform infrared emission spectra of BO were recorded using a Bruker IFS 125 HR spectrometer. The observed spectrum of BO in the 1200-2100 cm⁻¹ region contains three bands: the fundamental bands of ¹¹BO and ¹⁰BO and a hot band of ¹¹BO with band origins measured to be 1861.9242(97), 1915.3071(09) and 1838.3773(68) cm⁻¹, respectively.     

CW-cavity ringdown spectroscopy of carbon dioxide isotopologues near 1.5 μm

The absorption spectra of carbon dioxide in natural isotopic abundance and with 99% enrichment in ¹³C have been recorded by CW-cavity ringdown spectroscopy in two specific spectral regions: 5957-6122 and 6745-6833 cm⁻¹. The spectra were obtained at Doppler limited resolution by using a CW-CRDS spectrometer based on fibered DFB lasers. The typical sensitivity of 5 × 10⁻¹⁰ cm⁻¹, allowed for the detection of lines with intensity as weak as 5 × 10⁻²⁹ cm/molecule. More than 2900 line positions of the six major isotopologues contributing to the spectra (¹²C¹⁶O₂, ¹⁶O¹²C¹⁷O, ¹⁶O¹²C¹⁸O, ¹³C¹⁶O₂, ¹⁶O¹³C¹⁷O and ¹⁶O¹³C¹⁸O), were measured and assigned on the basis of their respective global effective Hamiltonian models. For comparison, only 507 lines are provided by the HITRAN database in these spectral regions. The band by band analysis has led to the determination of the rovibrational parameters of a total of 52 bands, 30 of them being newly reported. Most of the observed line positions show an agreement close to the experimental uncertainty (1-2 × 10⁻³ cm⁻¹) with the predictions of their respective effective Hamiltonian models. However, the quality of the predictions degrades for the minor isotopologues reaching maximum deviations of 0.35 cm⁻¹ in one specific case. For several bands, rovibrational transitions with J values between 60 and 90 could be newly detected. While an excellent agreement is observed with the line positions predicted by the Hamiltonian models, the comparison of these observations with the line positions listed in the HITRAN database or extrapolated by using the best FTS rotational constants available in the literature has evidenced significant deviations.     

ICLAS of weak transitions of water between 11 300 and 12 850 cm: Comparison with FTS databases

Very weak water vapor absorption lines have been investigated by intracavity laser absorption spectroscopy (ICLAS) in the 11 335-11 947 and 12 336-12 843 cm⁻¹ spectral regions dominated by the ν₁ + 3ν₂ + ν₃ and ν₂ + 3ν₃ bands, respectively. A detectivity on the order of α_min ∼ 10⁻⁹ cm⁻¹ was achieved with an ICLAS spectrometer based on a Ti: Sapphire laser. It allowed detecting transitions with an intensity down to 5 × 10⁻²⁸ cm/molecule which is about 10 times lower than the weakest line intensities previously detected in the considered region. A line list corresponding to 1281 transitions with intensity lower than 5 × 10⁻²⁶ cm/molecule has been generated. A detailed comparison with the line lists provided by the HITRAN database and by recent investigations by Fourier transform spectroscopy associated with very long multi pass cell is presented. The rovibrational assignment performed on the basis of the ab initio calculations of Schwenke and Partridge, has allowed for determining 176 new energy levels belonging to a total of 16 vibrational states.     

Fourier transform emission spectroscopy of the CΔ-XΦ, DΔ-XΦ, GΦ-XΦ and GΦ-CΔ systems of CoCl

The emission spectrum of CoCl has been recorded in the 2000-23 000 cm⁻¹ region at high resolution. CoCl was made in a carbon tube furnace by heating cobalt metal to a temperature of about 2300 °C as well as in a DC discharge source and the spectra were observed using a Fourier transform spectrometer. The bands observed in the 2000-13 000 cm⁻¹ interval have been classified into four transitions: C³Δ-X³Φ (2500-3600 cm⁻¹), D³Δ-X³Φ (9300-10 030 cm⁻¹), G³Φ-X³Φ (8500-13 000 cm⁻¹) and G³Φ-C³Δ (7400-7900 cm⁻¹) analogous to the near infrared transitions of CoF reported previously [R.S. Ram, P.F. Bernath, S.P. Davis, J. Chem. Phys. 104 (1996) 6949.]. A rotational analysis of a number of vibrational bands of these transitions has been obtained and spectroscopic constants extracted for the low-lying electronic states of CoCl. It is found that the energy levels of CoCl correlate very well with those of CoF and CoH.     

Line intensity measurements in N2O and their treatment using the effective dipole moment approach.II. The 5400-11 000 cm region

The absorption spectrum of N₂O, at room temperature, was recorded in the 5400-11 000 cm^-1 region at resolutions ranging from 0.008 cm^-1 near 5400 to 0.023 cm^-1 near 11 000 cm^-1 using a Bruker IFS120HR Fourier transform spectrometer. Sample pressure/absorption path length products ranging from 200 to 4700 mbar×m were used. More than 6000 absolute line intensities have been measured in 64 different bands of ¹⁴N₂¹⁶O. Using wavefunctions previously determined from a global fit of an effective Hamiltonian to more than 18 000 line positions [Tashkun SA, Perevalov VI, and Teffo JL, to be published], the experimental intensities measured in this work and by Toth [J Mol Spectrosc 1999;197:158-87] were fit using 62 parameters of a corresponding effective dipole moment, with residuals very close to the experimental uncertainty.     

Temperature dependence of the absorption spectrum of CH4 by high resolution spectroscopy at 81 K: (II) The icosad region (1.49-1.30 μm)

The high resolution absorption spectrum of methane has been recorded at liquid nitrogen temperature by differential absorption spectroscopy between 6717 and 7351 cm⁻¹ (1.49-1.36 μm) using a cryogenic cell and a series of distributed feed back (DFB) diode lasers. The investigated spectral region corresponds to the very congested low energy part of the icosad for which the HITRAN database provides neither rovibrational assignments nor the lower state energies. The positions and strengths at 81 K of 9389 transitions were obtained from the spectrum analysis. The minimum value of the measured line intensities (at 81 K) is on the order of 10⁻²⁶ cm/molecule. From the variation of the line strength between 81 K and 296 K, the low energy values of a total of 4646 transitions were determined. They represent 79.4% and 68.4% of the total absorbance in the region at 81 and 296 K, respectively, and include 28 transitions assigned to the ν₂+4ν₄ band near 6765 cm⁻¹. The reliability of the method based on the association of lines with coinciding centers in the 81 K and 296 K spectra is discussed. The results of the present analysis have been combined with previously analyzed high energy part of the icosad dominated by the ν₂+2ν₃ band near 7510 cm⁻¹. The line list for the whole icosad (6717-7655 cm⁻¹) consists of 12 865 transitions at 81 K.     

Water vapor absorption line intensities in the 1900-6600 cm region

Water vapor infrared spectra have been measured using the Bruker IFS 120 HR Fourier transform spectrometer at the Physikalisch-Chemisches Institut of the Justus-Liebig-Universität Giessen. Spectra were recorded at pressure-broadening-limited resolution and at room temperature in the range of 1900-6600 cm⁻¹. The use of fully evacuated transfer optics and a White-type multireflection cell made it possible to obtain pressure×pathlength products up to 31.27 mbar×288.5 m. These spectra have previously been used to determine experimental values of rovibrational line positions and upper energy levels of the 2ν₂, ν₁, and ν₃ bands [Mikhailenko SN, Tyuterev VlG, Keppler KA, Winnewisser BP, Winnewisser M, Mellau G, et. al. The 2ν₂ band of water: analysis of new FTS measurements and high-K_a transitions and energy levels. J Mol Spectrosc 1997;184: 330-49] and of the 3ν₂, ν₁+ν₂, and ν₂+ν₃ bands [Mikhailenko SN, Tyuterev VlG, Starikov VI, Albert KK, Winnewisser BP, Winnewisser M, et al. Water spectra in the region 4200-6250 cm⁻¹, extended analysis of ν₁+ν₂, ν₂+ν₃, and 3ν₂ bands and confirmation of highly excited states from flame spectra and from atmospheric long-path observations. J. Mol. Spectrosc. 2002; 213: 91-121].This work presents the intensities of 3769 lines for the weak and medium transitions in the spectral range indicated. These data provide an independent source of experimental information which is complementary to intensity data available in the literature and can thus help to evaluate experimental errors and the reliability of these spectral line parameters.     

Analysis of rotational structure in the high-resolution infrared spectrum and assignment of vibrational fundamentals of butadiene-2,3-C2

The 2,3-¹³C₂ isotopomer of butadiene was synthesized, and its fundamental vibrational fundamentals were assigned from a study of its infrared and Raman spectra aided with quantum chemical predictions of frequencies, intensities, and Raman depolarization ratios. For two C-type bands in the high-resolution (0.002 cm⁻¹) infrared spectrum, the rotational structure was analyzed. These bands are for ν₁₁ (a_u) at 907.17 cm⁻¹ and for ν₁₂ (a_u) at 523.37 cm⁻¹. Ground state and upper state rotational constants were fitted to Watson-type Hamiltonians with a full quartic set of centrifugal distortion constants and two sextic ones. For the ground state, A₀ = 1.3545088(7) cm⁻¹, B₀ = 0.1469404(1) cm⁻¹, and C₀ = 0.1325838(2)  cm⁻¹. The small inertial defects of butadiene and two ¹³C₂ isotopomers, as well as for five deuterium isotopomers as previously reported, confirm the planarity of the s-trans rotamer of butadiene.     

Determination of the low energy values of CH4 transitions in the 2ν3 region near 1.66 μm from absorption spectra at 296 and 81 K

The high resolution absorption spectra of ¹³CH₄ were recorded at 81 K by differential absorption spectroscopy using a cryogenic cell and a series of distributed feed back (DFB) diode lasers and at room temperature by Fourier transform spectroscopy. The investigated spectral region corresponds to the high energy part of the ¹³CH₄ tetradecad dominated by the 2ν₃ overtone near 5988 cm⁻¹. Empirical line lists were constructed containing, respectively, 1629 ¹³CH₄ transitions detected at 81 K (5852-6124 cm⁻¹) and 3481 features (including 85 lines of ¹²CH₄) measured at room temperature (5850-6150 cm⁻¹); the smallest measured intensities are about 3 × 10⁻²⁶ and 4 × 10⁻²⁵ cm/molecule at 81 and 296 K, respectively. The lower state energy values were derived for 1196 ¹³CH₄ transitions from the variation of the line intensities between 81 and 296 K. These transitions represent 99.2% and 84.6% of the total absorbance in the region, at 81 and 296 K, respectively. Over 400 additional weak features were measured at 81 K and could not be matched to lines observed at room temperature. The quality of the resulting empirical low energy values is demonstrated by the excellent agreement with the already-assigned transitions and the clear propensity of the empirical low J values to be close to integers. The two line lists at 81 and at 296 K provided as Supplementary material will enable future theoretical analyses of the upper ¹³CH₄ tetradecad.