Measurements of O2-broadening and -shifting parameters of water vapor spectral lines in the second hexad region

Oxygen pressure induced broadening and shifting coefficients for water vapor absorption lines in the 8600–9010 cm⁻¹ region have been measured and calculated. The spectra were recorded with a Bruker IFS 125HR spectrometer at a spectral resolution of 0.01 cm⁻¹ for lines with angular moment of the upper states up to 10. Calculations of line broadening and shifting coefficients are performed using a semi-empirical approach. The method is based on the impact theory of broadening, and includes the correction factors whose parameters can be determined by fitting the broadening or shifting coefficients to the experimental data. The comparison of our calculations with the experimental values argues that the semi-empirical method is quite acceptable for the determination of the water vapor absorption line profile parameters.     

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.     

Water vapor line width and shift calculations with accurate vibration-rotation wave functions

Calculations of H₂¹⁶O rotation-vibration line broadening and shifting due to N₂ pressure effects are performed using a semi-empirical approach. The calculations are based on impact theory modified by introducing additional parameters to extend the use of empirical data. These model parameters are determined by fitting the broadening and shifting coefficients to experimental data. The method is further developed by using anharmonic wavefunctions in the estimates of the line profiles. The main feature of the present calculation is the use of a complete set of high-accuracy vibration-rotation dipole transition moments calculated for all possible transitions using wavefunctions determined from variational nuclear motion calculations and an ab initio dipole moment surface. This approach explicitly takes into account all scattering channels induced by collisions. Results of these calculations clearly demonstrate improved agreement between observed and calculated parameters for both the line widths and the line shifts.     

Measurements of N2-broadening and -shifting parameters of the water vapor spectral lines in the second hexad region

The water vapor line broadening and shifting in the ν₁+ν₂+ν₃ band induced by nitrogen pressure are measured with Bruker IFS 125 HR FTIR spectrometer at the spectral resolution of 0.01 cm⁻¹ for the line with upper states angular momentum up to 11. Line contour parameters are calculated using a semi-empirical approach extended by the use of empirical data to determine some fitting model parameters. We use the complete set of high accuracy vibration-rotation dipole transition moments calculated for all possible transitions using wavefunctions determined from variational nuclear motion calculations and an ab initio dipole moment surface. Calculated values of line contour parameters are in a good agreement with observed parameters.     

Comparison between theoretical calculations and high-resolution measurements of pressure broadening for near-infrared water spectra

We report N₂ and air foreign pressure broadening coefficients of more than twenty rovibrational transitions of water vapor in the 935-nm spectral region, and these measurements are compared to new theoretical calculations. The data were obtained using the frequency-stabilized cavity ring-down spectroscopy method, yielding relative uncertainties for the broadening parameters in the range 0.4-2.2%. The sensitivity of measured broadening parameters to the choice of line shape functions is discussed, and systematic differences between experimentally determined collisional broadening coefficients are shown for the cases when the observed line narrowing is interpreted in terms of Dicke-narrowing or the speed-dependence of the collisional broadening and shifting. Theoretical models of pressure broadening for these transitions agree with the measurements to within 4% for most transitions with an average relative difference of 0.63%.     

Measurements and calculations of He-broadening and -shifting parameters of the water vapor transitions of the ν 1 + ν 2 + ν 3 band

The water vapor line broadening and shift in the ν ₁?+?ν ₂?+?ν ₃ band induced by helium pressure were measured using a Bruker IFS 125HR FTIR spectrometer. The measurements were performed at room temperature at a spectral resolution of 0.01?cm^?1 and in a wide He pressure range. The shifting coefficients δ are mainly positive, in contrast to the line center shift induced by other mono-atomic gases. Calculations of the coefficients γ and δ were performed in the framework of the semi-classical method. The influence of the rotational dependence of the isotropic intermolecular potential and accidental resonances in the H₂O molecule on the shifting coefficients is discussed. Calculated values of line profile parameters are in a good agreement with observed parameters.     

Self and N2 collisional broadening of far-infrared methane lines measured at the SOLEIL synchrotron

Following our recent study devoted to measurements of intensities of pure rotation lines of methane, room temperature far infrared spectra of methane diluted in nitrogen at five total pressures between 100 and 800 hPa have been recorded at the AILES beamline of the SOLEIL synchrotron. One hundred and five N₂ broadening coefficients of methane pure rotation lines have been measured in the 83–261 cm^?1 spectral range using multi-spectrum non-linear least squares fitting of Voigt profiles. Pressure-induced line shifts were not needed to fit the spectra to the noise level and line mixing effects were neglected. One hundred and seventy-six self broadening coefficients have also been measured in the 59–288 cm^?1 spectral range using the pure methane spectra recorded in our previous work. The measured N₂ broadening coefficients were compared to semi-classical calculations.     

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.     

Diode laser spectroscopy of He,N2 and air broadened water vapour transitions belonging to the (2ν1 + ν2 + ν3) overtone band

The line shape parameters of rovibrational transitions of water vapour belonging to the (2ν₁ + ν₂ + ν₃) overtone band due to collisions between absorber molecules and noble gas helium have been measured in the spectral range between 11988.494 cm^?1 and 12218.829 cm^?1 using NIR diode laser spectrometer. In addition nitrogen and air broadening effects on some water vapour transitions belonging to the same band have also been studied. Wavelength modulation spectroscopy along with phase sensitive detection technique are used to record first derivative (1f) signal of buffer gas broadened water vapour transitions. Observed line shapes are fitted to standard Voigt profiles by non-linear least squares fitting program to extract the line shape parameters, like line strength and pressure broadening coefficients. The broadening effects induced by different types of buffer gases on water vapour line shapes are compared. Rotational quantum number (J) dependence of broadening coefficients of water vapour transitions is also examined.     

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.     

Collisional broadening and line intensities in the ν2 and ν4 bands of PH3

Using a tunable diode-laser spectrometer self-broadening coefficients and absolute intensities have been measured for 26 lines of PH₃ at 298 K in the QR branch of the ν₂ band and the PP and RP branches of the ν₄ band. The recorded lines with J values ranging from 2 to 14 and K from 0 to 11 are located in the spectral range 995-1093 cm⁻¹. Self-broadening coefficients have also been measured at 173.4 K for nine of these lines. The collisional widths and line strengths are obtained by fitting each spectral line with different theoretical profiles. The results obtained for the line intensities are in good agreement with recent measurements [J. Mol. Spectrosc. 215 (2002) 178]. The self-broadening coefficients are also calculated on the basis of a simple semiclassical model involving only the electrostatic interactions. A satisfactory agreement is obtained except for high J values or K values equal to J, for which the calculated results are notably underestimated. By comparing broadening coefficients at room and low temperatures, the temperature dependence of these broadenings has been determined both experimentally and theoretically.     

Measurements and calculations of H2-broadening and shifting parameters of water vapour transitions in a wide spectral region

ABSTRACT

The water vapour line broadening (γ) and shifting (δ) coefficients for 149 lines of 10 vibrational bands 2ν₁, 2ν₃, ν₁?+?ν₃, 2ν₂?+?ν₃, ν₁?+?2ν₂, ν₂?+?2ν₃, 2ν₁?+?ν₂, 3ν₂?+?ν₃, ν₁?+?3ν₂ and 6ν₂ induced by hydrogen pressure were measured with a Bruker IFS 125 HR spectrometer. The measurements were performed at room temperature with a spectral resolution of 0.01 cm^–1 and in a wide pressure range of H₂. The calculations of the broadening coefficients γ and δ were performed in the framework of the semi-classical method using an effective vibrationally dependent interaction potential. The optimal sets of potential parameters that give the best agreement with the measured broadening coefficients for each vibrational band separately were found. Then combined experimental data of 16 vibrational bands of H₂O perturbed by H₂ were used to determine the analytical dependence of some potential parameters on vibrational quantum numbers. The analytical expressions that reproduce the broadening coefficients γ for different vibrational bands are proposed.     

Collisional parameters of H2O lines: Velocity effects on the line-shape

This paper is devoted to the effects of velocity on the shapes of six R(J) lines of the ν₃ band of water vapor diluted in N₂. The experiments have been made at room temperature for total pressures between 0.1 and 1.2 atm using a tunable infrared laser frequency difference spectrometer. These measurements, which study broad and narrow lines of low and high J values, are first analyzed using the Voigt and the hard collision (HC) model. It is shown that both lead to unsatisfactory results, the Voigt profile being unable to account for the line narrowing whereas the friction (narrowing) parameter deduced using the HC approach has an unphysical dependence on pressure. Furthermore, at elevated pressure where Dicke narrowing and Doppler effects are negligible, deviations between experimental and fitted profiles are still observed, indicating inhomogeneous effects due to the speed dependence of collisional parameters. In order to go further, an approach based on the kinetic impact equation accounting for both the Dicke narrowing and the speed dependence has been applied. It uses velocity-dependent broadening and shifting coefficients calculated with a semi-classical approach and two parameters. The latter, which govern the memory functions of the modulus and orientation of the H₂O velocity are considered as free parameters and determined from experiments. The results show that all profiles, regardless of pressure and of the transition, can be correctly modeled using a single set of memory parameters. This demonstrates the consistency of the approach, which is then used to analyze the different regimes that monitor velocity effects on the line profile.     

H2-broadening,shifting and mixing coefficients of the doublets in the ν2 and ν4 bands of PH3 at room temperature

The broadening, shifting and mixing coefficients of the doublet spectral lines in the ν₂ and ν₄ bands of PH₃ perturbed by H₂ have been determined at room temperature. Indeed, the collisional spectroscopic parameters: intensities, line widths, line shifts and line mixing parameters, are all grouped together in the collisional relaxation matrix. To analyse the collisional process and physical effects on spectra of phosphine (PH₃), we have used the measurements carried out using a tunable diode-laser spectrometer in the ν₂ and ν₄ bands of PH₃ perturbed by hydrogen (H₂) at room temperature. The recorded spectra are fitted by the Voigt profile and the speed-dependent uncorrelated hard collision model of Rautian and Sobelman. These profiles are developed in the studies of isolated lines and are modified to account for the line mixing effects in the overlapping lines. The line widths, line shifts and line mixing parameters are given for six A₁ and A₂ doublet lines with quantum numbers K = 3n,?(n = 1,?2, …) and overlapped by collisional broadening at pressures of less than 50 mbar.     

Shifting and line mixing parameters in the ν4 band of NH3 perturbed by CO2 and He: Experimental results and theoretical calculations

The pressure-induced shifting coefficients and line mixing parameters have been studied in the ν₄ band of NH₃ perturbed by CO₂ and He at room temperature. Measurements have been made using a high-resolution Fourier transform spectrometer. The measurements cover the ^PP and ^RP branches of the ν₄ band and are located in the spectral range 1470-1600 cm⁻¹. The line shift and line mixing parameters have been derived from a non-linear least-squares multi-pressure fitting technique. The shift coefficients are compared to a semiclassical calculation based on the Robert-Bonamy formalism employing two types of intermolecular interactions. It is shown that the line shifts mainly originate from the vibrational dephasing effects. The observed interference parameters are compared with calculations based on state-to-state collisional cross sections calculated from the intermolecular potential with a semiclassical approach. The results of computation are in reasonable agreement with the experimental data. It is demonstrated also that the line mixing process mainly originates from the energy transfer between symmetric and antisymmetric components of the inversion doublets.     

Stark-Effekt-Verbreiterung der Neon I-Übergänge mit schwacher Feldstärkeabhängigkeit (2p 5 3s-2p 5 3p)

The half widths of Stark-broadened Ne I spectral lines (2p ⁵ 3s-2p ⁵ 3p) were measured in wall stabilized arc plasmas (pressurep=1 atm, andp=3 atm) consisting of several gas components (Ar 68%, Ne 27%, He 3%, H₂ 2%). The theoretical half widths of two spectral lines (λ=6,266.50 Å,λ=6,163.59 Å) with known calculated broadening parameters according to Griem differ by a factor 1.8 to 1.9 from the measured widths. Within the errors of Griem's line broadening calculations of about 20% there was agreement between experimental and theoretical half widths regarding two other spectral lines (λ=5,881.90 Å,λ=5,852.49 Å). Calculated adiabatic widths are smaller than the widths according to Griem. Therefore in some cases the deviation of the adiabatic widths from the measured widths is smaller than the difference between Griem widths and experimental ones. Static quadratic coefficients of NeI transitions 2p ⁵ 3s-2p ⁵ 3p calculated from measured Stark-broadened lines showed wavelength displacements in the order of 0.005 Å referring to an electrical field of 100 kV/cm. The determined coefficients are 10² times smaller than those values measurable by known methods of emission spectroscopy.     

Studies of 183 GHz water line: broadening and shifting by air, N2 and O2 and integral intensity measurements

The 3₁₃-2₂₀ rotational transition of water vapor at 183 GHz was studied using modern resonator spectroscopy methods at atmospheric pressures in the broad frequency range 130-205 GHz down to far wings. The experimental method of sample substitution for the exclusion of the apparatus function was used. The air broadening parameter value was defined as 3.84±0.04 MHz/Torr at 298 K. The observed atmosphere water vapor line center was found to be shifted down at about 53 MHz from the line center at low pressures, which gives a value of −0.07±0.02 MHz/Torr for the air pressure shift parameter. Measurements of broadening and shifting of the water line in pure nitrogen and oxygen atmosphere were also performed. Calculated then parameters of air broadening and shifting agree with directly measured ones within the errors quoted. Measurement of the integral intensity of the line was done. The directly measured integral line intensity coincides with a value given in GEISA and HITRAN databases within experimental error. The results are compared with previous experimental laboratory and satellite data.     

H2 vibrational spectral signatures in binary and ternary mixtures: theoretical model,simulation and application to CARS thermometry in high pressure flames

A summary of the main results obtained by the two groups in the field of H₂ vibrational spectral line signatures for various mixtures, in connection with CARS diagnostics of H₂–O₂ combustion systems, is presented. H₂–X systems may have specific large inhomogeneous spectral features, due to the dependence of the line broadening and line shifting on the (H₂) radiator speed, particularly at high temperature. Thus, careful attention has to be paid to rigorously analyze such features, both from the experimental point of view (Dijon) and from the theoretical one (Besançon). Applications of the present results to high-pressure H₂/air flame thermometry are also briefly described. They present an approach aiming to include the more recent basic results on coherent Raman line shape in CARS diagnostics, in order to improve the accuracy of temperature measurements.     

N2- and O2-broadening coefficients in the ν2 and ν5 bands of CH3F at 183 and 298 K

The N₂- and O₂-broadening coefficients of 33 rovibrational lines in the ν₂ and ν₅ bands of ¹²CH₃F were measured at 183 K using a diode-laser spectrometer. The measurement of these coefficients was also realized at room temperature for 10 of these lines to determine their temperature dependence. The line parameters were obtained by fitting to the experimental profile the Voigt lineshape, and the Rautian and Galatry models taking into account the collisional narrowing. Calculations of the pressure-broadening coefficients were also performed for the same temperatures from a semiclassical model involving electrostatic, induction and dispersion interactions in the intermolecular potential. The calculated values reproduce well the experimental data for both temperatures and both perturbers and the theoretical temperature dependence of the broadening coefficients is in satisfactory agreement with that derived from the measurements.