Pressure broadening coefficients of the water vapor lines at 556.936 and 752.033 GHz

The air induced broadening coefficients of the pure rotational transitions of H₂O at 556.936 GHz (1₁₀←1₀₁), and 752.033 GHz (2₁₁←2₀₂) were measured by terahertz time-domain spectroscopy. The air broadening coefficient was determined to be for the 556.936 GHz line and for the 752.033 GHz line, respectively. The present broadening coefficients for the 556.936 GHz water line are significantly smaller than those of Markov and Krupnov [Measurements of the pressure shift of the 1(10)-1(01) water line at 556.936 GHz produced by mixtures of gases. J Mol Spect 1995:172;211-4] but relatively close to the values of the HITRAN database. The measured data may improve the accuracy of the abundance of water vapor retrieved from spectra obtained by the Odin/SMR satellite instrument. The effect on the satellite retrieval processing is discussed.     

Line shift and mixing in the ν4 and 2ν2 band of NH3 perturbed by H2 and Ar

Pressure induced line shift and line mixing parameters have been measured for 66 rovibrational lines in the ν₄ band and for 10 lines in the 2ν₂ band of NH₃ perturbed by H₂ and Ar at room temperature (T = 296 K). These lines with J values ranging from 2 to 10 are located in the spectral range 1450-1600 cm⁻¹. Experiments were made with a high-resolution Fourier transform spectrometer. The line shifts and line mixing parameters have been derived from the non-linear least-square multi-pressure fitting technique. The shift coefficients are compared with those calculated from the Robert-Bonamy formalism (RB). The results are generally in satisfactory agreement with the experimental data.     

Absorption profiles of HCl for the J = 1-0 rotational transition: Foreign-gas effects measured for N2, O2, and Ar

Line profiles of the J = 1-0 transition of the hydrogen chloride, H³⁵Cl and H³⁷Cl isotopomers, were measured with a BWO-based submillimeter-wave spectrometer at AIST in real form: three hyperfine transitions for each isotopomer, i.e., total six lines at 625 and 626 GHz. The effect of foreign gases on the broadening and shift was determined for N₂, O₂, and Ar. The modified Voigt function was applied as the line shape function for preliminary analysis, where the collisional-narrowing effect was clearly observed. In the final analysis, we applied the Galatry function and determined the integral intensity, line center position, Lorentzian width, and contraction parameter for each absorption line. The magnitudes of the foreign-gas pressure-broadening coefficients decrease in order of N₂, O₂, and Ar. The line-shift coefficients were clearly observed, the magnitudes of which decrease in order of Ar, O₂, and N₂. The pressure dependence of contraction parameter was determined, although with poor precision.     

Ar-Broadening of isotropic Raman lines in the ν2 band of acetylene

Using a high resolution Raman spectrometer, we have measured Ar-broadening coefficients in the ν₂Q branch of C₂H₂ for 22 lines at 295 K, 20 lines at 174 K, and 16 lines at 134 K. These lines with J values ranging from 1 to 23 are located in the spectral range 1970.9-1974.3 cm⁻¹. The collisional widths are obtained by fitting each spectral line with a Rautian profile. The resulting broadening coefficients are compared with theoretical values arising from close coupling and coupled states calculations. A satisfactory agreement is obtained at room as well as at low temperatures, especially for odd J lines. By comparing broadening coefficients at 295, 174, and 134 K from a simple power law, the temperature dependence of these broadenings has been determined both experimentally, and theoretically.     

Line broadening and shift coefficients of acetylene at 1550 nm

Pressure broadening and shift coefficients have been measured for the ν₁ + ν₃ band of acetylene, C₂H₂, broadened by N₂, H₂, D₂, air, and the noble gases at 295 K. Coefficients are reported for lines between 6470 and 6612 cm⁻¹ (1512-1546 nm). The pressure broadening coefficients are in general agreement with those reported for other vibrational bands, indicating that they are insensitive to vibrational excitation. The pressure shift coefficients, by contrast, are found to differ substantially among vibrational bands.     

The rotationally-resolved absorption spectrum of formaldehyde from 6547 to 6804 cm

The room temperature absorption spectrum of formaldehyde, H₂CO, from 6547 to 6804 cm⁻¹ (1527-1470 nm) is reported with a spectral resolution of 0.001 cm⁻¹. The spectrum was measured using cavity-enhanced absorption spectroscopy (CEAS) and absorption cross-sections were calculated after calibrating the system using known absorption lines of H₂O and CO₂. Several vibrational combination bands occur in this region and give rise to a congested spectrum with over 8000 lines observed. Pressure broadening coefficients in N₂, O₂, and H₂CO are reported for an absorption line at 6780.871 cm⁻¹, and in N₂ for an absorption line at 6684.053 cm⁻¹.     

Line mixing effects in the ν2 + ν3 band of methane

This study provides the first direct experimental measurements of the off-diagonal relaxation matrix element coefficients for line mixing in air-broadened methane spectra for any vibrational band and the first off diagonal relaxation matrix elements associated with line mixing for pure methane in the ν₂ + ν₃ band of ¹²CH₄. The speed-dependent Voigt profile with line mixing is used with a multispectrum nonlinear least squares curve fitting technique to retrieve the various line parameters from 11 self-broadened and 10 air-broadened spectra simultaneously. The room temperature spectra analyzed in this work are recorded at 0.011 cm⁻¹ resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory, Kitt Peak, Arizona. The off-diagonal relaxation matrix element coefficients of ν₂ + ν₃ transitions between 4410 and 4629 cm⁻¹ are reported for eighteen pairs with upper state J values between 2 and 11. The observed line mixing coefficients for self broadening vary from 0.0019 to 0.0390 cm⁻¹ atm⁻¹ at 296 K. The measured line mixing coefficients for air broadening vary from 0.0005 to 0.0205 cm⁻¹ atm⁻¹ at 296 K.     

Argon-broadening coefficients in the ν5 band of acetylene at room and low temperatures

Ar-broadening coefficients have been measured in the P- and R-branches of the ν₅ fundamental band of C₂H₂ for 30 lines at room temperature and 8 lines at −100 °C, using a tunable diode-laser spectrometer. These lines with J values ranging from 2 to 27 are located in the spectral range 665-795 cm⁻¹. The collisional widths are obtained by fitting each absorption line with three lineshape models: the Voigt profile, the Rautian profile accounting for the Dicke narrowing effect, and a general Rautian profile including the absorber speed-dependent collisional broadening. The latter model provides significantly larger broadening coefficients than the Voigt model. These coefficients are also calculated from a semiclassical theory performed by using a simple intermolecular potential with two adjustable parameters. Finally, the temperature dependence of the broadening coefficients has been determined both experimentally and theoretically.     

N2Broadening in theCO 2–0 Band around 4167 cm

N₂broadening coefficients have been measured for 65 lines of the¹³C¹⁶O 2–0 band using a Fourier transform spectrometer. These lines are located in the spectral range 4011–4252 cm⁻¹. The spectra were recorded with 99% isotopically pure¹³CO in a White-type cell at a resolution of 0.005 cm⁻¹. Voigt profiles convolved with the FTS apparatus function were fitted to the experimental lineshapes using a nonlinear least-squares fit technique. From the fits the Lorentzian HWHM was determined as function of N₂pressure. Pressure broadening coefficients formbetween −33 and +34 were obtained with uncertainties of 5.8%. The results are compared to earlier published N₂broadening coefficients and our measurements in the 2–0 band of¹²C¹⁶O. To our knowledge this is the first investigation of¹³CO pressure broadening.     

Diode laser measurements of temperature-dependent collisional-narrowing and broadening parameters of Ar-perturbed H2O transitions at 1391.7 and 1397.8 nm

High-resolution absorption lineshapes of two H₂O transitions near 7185.60 and 7154.35 cm⁻¹ have been recorded in a heated static cell as a function of temperature (296-1100 K) and pressure (6-830 Torr) using two distributed-feedback diode lasers. The measured absorption spectra are least squares fit to both Voigt and Galatry profiles. Strong collisional-narrowing effects are observed in the Ar-broadened H₂O spectra at near-atmospheric pressure due to the relatively weak collisional broadening induced by Ar-H₂O collisions, while collisional narrowing is not significant for pure H₂O absorption lineshapes. Line strengths and self-broadening coefficients are inferred from the pure H₂O absorption spectra and compared with published data. Temperature dependences of the Ar-induced broadening, narrowing, and shift coefficients are determined using Galatry fits to the absorption data. The measured collisional-narrowing parameters have similar temperature dependence to the collisional-broadening coefficients.     

Air pressure broadening and shifting of high-J lines of (00011) ← (00001) band of CO2

The absorption spectra of carbon dioxide (isotope 626, natural abundance in air, ambient temperature) have been studied at total pressures 68-570 Torr with spectral resolution 0.003-0.005 cm⁻¹. The spectra were measured in the spectral domain of 2273-2393 cm⁻¹ by FTIR spectrometer Bruker IFS 125 HR equipped with White-type multipass cell (6.4-41.6 m) and with a cell having 10 cm optical path length. Pressure broadening and shift coefficients were obtained from a series of spectra by means of a nonlinear least-squares spectral fitting technique for the lines of the (00011)←(00001) band with rotational quantum number up to J=82. For fitting of the individual line shapes, we used the Voigt profile with pre-calculated Doppler broadening parameter. The experimental pressure broadening and shift coefficients are compared with the values available in spectroscopic databases HITRAN 2008 and Carbon Dioxide Spectroscopic Databank (CDSD-296) and with other experimental values reported in the literature.     

Linewidth and intensity measurements of SO2 lines at 94 GHz with self-broadening and broadening by H2O and N2

In the frequency range between 91.5 and 95.5 GHz, three rotational lines of the ³²S¹⁶O₂ and two rotational lines of the ³⁴S¹⁶O₂ molecules in the fundamental vibrational state, and also two lines of the ³²S¹⁶O₂ molecule in the v₂ vibrational state, have been investigated. Center frequencies and absolute absorptions have been measured and compared with theoretical values. Furthermore, the self-broadening and broadening by H₂O and N₂ of the transition 23(6,18)–24(5,19) with the line center at 94.064 GHz have been investigated. The following linewidth parameters were found: SO₂-SO₂, 18.2±0.3 MHz/torr; SO₂-N₂, 3.8±0.1 MHz/torr; SO₂-H₂O, 15.2±0.2 MHz/torr. The bridge spectrometer and the measuring method used are also described.     

Collisional broadening and shifting of the 211-202 transition of H2O, H2O, H2O by atmosphere gases

Broadening and shifting of the 2₁₁-2₀₂ transition of H₂¹⁶O, H₂¹⁷O, H₂¹⁸O by pressure of water, nitrogen and oxygen were precisely measured at room temperature using spectrometer with radio-acoustic detection of absorption. Shift parameters for all studied lines as well as broadening parameters of H₂¹⁷O, H₂¹⁸O lines were measured for the first time. Comparison of obtained results with previously known experimental and theoretical data is presented.     

Air-broadening parameters in the ν3 band of NO2 using a multispectrum fitting technique

Air-broadened linewidths, pressure-induced shift coefficients and their temperature dependences were retrieved for over 1000 transitions in the ν₃ band of ¹⁴N¹⁶O₂ at 6 μm. In addition, precise line center positions and relative intensities were also determined. The results were obtained by fitting simultaneously 27 spectra recorded at high resolution (0.002-0.006 cm⁻¹) with two Fourier transform spectrometers and gas sample temperatures ranging from 206 to 298 K. It was necessary to modify the multispectrum fitting software to accommodate constraints on the retrieved parameters of closely spaced spin-split doublets in order to successfully determine their broadening and shift parameters. The variations of the widths, shifts and their temperature dependences with the quantum numbers were investigated. Subsets of the observed linewidths were reproduced to within 3% using an empirical smoothing function.     

Hydrogen line broadening in the ν2 and ν4 bands of phosphine at low temperature

Using a tunable diode-laser spectrometer, we have measured H₂-broadening coefficients of PH₃ at low temperature (173.2 K) for 27 lines in the ^QR branch of the ν₂ band and in the ^PP and ^RP branches of the ν₄ band. The recorded lines with J values ranging from 2 to 11 and K from 0 to 9 are located between 1016 and 1093 cm⁻¹. The collisional widths are determined by fitting each spectral line with a Voigt profile and a speed-dependent Rautian profile which provides slightly larger broadening coefficients than the Voigt model. These coefficients have also been calculated on the basis of a semiclassical model of interacting linear molecules by considering an atom-atom Lennard-Jones potential in addition to the weak electrostatic contributions. Except for three ^QR(J,K) lines, where K = J, the calculated broadening coefficients are in good agreement with the experimental data. By comparing the results obtained at room and low temperatures, the temperature dependence of linewidths has been determined both theoretically and experimentally.     

Self-, N2- and O2-broadening coefficients for the CO2 transitions near-IR measured by a diode laser photoacoustic spectrometer

Using a high-resolution tunable diode laser photoacoustic spectrometer, self-, N₂ and O₂ pressure broadening coefficients for the first 11 transitions of ¹²C¹⁶O₂ in the R branch of the (30012) ← (00001) overtone band at the 6348 cm⁻¹ have been revisited at room temperature (∼298 K). Air-broadening parameters have also been calculated from the N₂ and O₂ measurements. The dependence of the broadening on rotational quantum number m is discussed. The recorded lineshapes are fitted with standard Voigt line profiles in order to determine the collisional broadening coefficients of carbon dioxide transitions. The results are compared to our previous measurements and to the values reported in the HITRAN04 database and by other research group with a different spectroscopic technique.     

A multispectrum analysis of the ν2 band of HCN: Part I. Intensities, broadening, and shift coefficients

Absolute intensities, self- and air-broadening coefficients, self- and air-induced shift coefficients and their temperature dependences have been determined for lines belonging to the P- and R-branches of the ν₂ band of H¹²C¹⁴N centered near 712 cm⁻¹. Infrared spectra of HCN in the 14-μm region were obtained at high resolution (0.002-0.008 cm⁻¹) using two different Fourier transform spectrometers (FTS), the McMath-Pierce FTS at the National Solar Observatory on Kitt Peak and the Bruker IFS 120HR FTS at the Pacific Northwest National Laboratory. Spectra were recorded with 99.8% pure HCN as well as lean mixtures of HCN in air at various temperatures ranging between +26 and −60 °C. A multispectrum nonlinear least squares technique was used to fit selected intervals of 36 spectra simultaneously to obtain the line positions, intensities, broadening, and shift parameters. The measured line intensities were analyzed to determine the vibrational band intensity and the Herman-Wallis coefficients. The measured self-broadening coefficients vary between 0.2 and 1.2 cm⁻¹ atm⁻¹ at 296 K, and the air-broadening coefficients range from 0.08 to 0.14 cm⁻¹ atm⁻¹ at 296 K. The temperature dependence exponents of self-broadening range from 1.46 to −0.12 while the corresponding exponents for air broadening vary between 0.58 and 0.86. The present measurements are the first known determination of negative values for the temperature dependence exponents of HCN-broadening coefficients. We were able to support our self-broadening measurements with appropriate theoretical calculations. Our present measurements are compared, where possible, with previous measurements for this and other HCN bands, as well as the parameters that are included in the 2000 and 2004 editions of the high-resolution transmission (HITRAN) database.     

Diode-laser measurements of O2, N2 and air-pressure broadening and shifting of NH3 in the 10 μm spectral region

Using a tunable diode-laser spectrometer, we have measured the O₂, N₂, air-shift and broadening coefficients for 5 lines of ammonia in the R branch of the ν₂ band. These lines are located in the spectral range 1030-1070 cm⁻¹. The pressure shift and broadening are obtained by fitting the measured shapes of these lines by a Voigt profile. The broadening parameters and shift coefficients are compared to the results of theoretical calculations based on the semiclassical Robert-Bonamy formalism (RB) in which the intermolecular potential includes electrostatic, induction, and dispersion energy contributions. The variation of these coefficients with rotational and vibrational quantum numbers is examined. The results are generally in satisfactory agreement with experimental data.     

Intensity measurements of H2O lines in the spectral region 8000-9350 cm

This paper presents new measurements of H₂¹⁶O lines performed on spectra recorded with the GSMA Fourier Transform Spectrometer (FTS). Our experimental conditions allow one to obtain new line intensity measurements from 10⁻²⁵ to 10⁻²¹ cm/molec at 296 K and self-broadening coefficients in the spectral range centered at 8800 cm⁻¹. In the HITRAN database, data reported for this region is taken from the work of Mandin et al. (1988) [8] and [9] and several articles pointed out problems on the line intensities. We present in this paper some intensity comparisons, first with the HITRAN database, and then with the recent article of Tolchenov and Tennyson (2005) [3]. We finish by a comparison on self-broadening coefficients.     

High sensitivity ICLAS of H2O in the 12,580-13,550 cm transparency window

High-sensitivity Intracavity Laser Absorption Spectroscopy (ICLAS) is used to measure the high resolution absorption spectrum of H₂¹⁸O between 12,580 and 13,550 cm⁻¹. This spectral region covers the 3v+δ polyad of very weak absorption. Four isotopologues of water (H₂¹⁸O, H₂¹⁶O, H₂¹⁷O, HD¹⁸O) are found to contribute to the observed spectrum. Spectrum analysis is performed with the aid of variational calculations and allowed for assigning 1126 lines belonging to H₂¹⁸O, while only 160 H₂¹⁸O lines are included in the HITRAN-2008 database. Altogether, 823 accurate energy levels of H₂¹⁸O are determined from transitions attributed to 26 upper vibrational states, 438 of them being reported for the first time. New information includes energy levels of four newly observed vibrational states of H₂¹⁸O: (2 4 0), (1 4 1), (0 4 2) and (2 3 1) at 13,167.718, 13,212.678, 13,403.71 and 15,073.975 cm⁻¹, respectively. H₂¹⁸O transitions involving highly excited bending states like (1 6 0), (0 6 1), (0 7 1), (1 7 0), (0 9 0) and even (0 10 0) have been identified as a result of an intensity borrowing from stronger bands via high-order resonance interactions. Thirty-six new energy levels of H₂¹⁷O, present with a 2% relative concentration in our sample, could be determined. The rotational structure of the (0 2 3) state of HD¹⁸O at 13,245.497 cm⁻¹ is also reported for the first time.