Experimental Air-Broadened Line Parameters in the nu2 Band of CH3D

In this study we report the first experimental measurements of air-broadening and air-induced pressure-shift coefficients for approximately 378 transitions in the nu2 fundamental band of CH3D. These results were obtained from analysis of 17 room temperature laboratory absorption spectra recorded at 0.0056 cm(exp -1) resolution using the McMath-Pierce Fourier transform spectrometer located on Kitt Peak, Arizona. Three absorption cells with path lengths of 10.2, 25 and 150 cm were used to record the spectra. The total sample pressures ranged from 0.129x10(exp -2) to 52.855x10(exp -2) atm with CH3D volume mixing ratios of approximately 0.0109 in air. The spectra were analyzed using a multispectrum non-linear least-squares fitting technique. We report measurements for air pressure-broadening coefficients for transitions with quantum numbers as high as J" = 20 and K = 15, where K" = K' equivalent to K (for a parallel band). The measured air broadening coefficients range from 0.0205 to 0.0835 cm(exp -1) atm(exp -1) at 296 K. All the measured pressure-shift coefficients are negative and are found to vary from about -0.0005 to -0.0080 cm(exp -1) atm(exp -1) at the temperature of the spectra. We have examined the dependence of the measured broadening and shift parameters on the J" and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = -J", J" and J" + 1 in the (sup Q)P- (sup Q)Q-, and (sup Q)R-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.4%

Low pressure line shape study of nitrogen-perturbed acetylene transitions in the ν1 + ν3 band over a range of temperatures

International audienceSix nitrogen perturbed transitions of acetylene within the ν1+ν3 absorption band have been recorded using a 3-channel diode laser spectrometer. The goal being an improved understanding of both broadening and narrowing effects of low pressure acetylene under the influence of nitrogen gas. To this end we have examined C2H2 spectra using a hard collision Rautian profile over a range of five temperatures (213 K-333 K) and five pressures (5-40 Torr). From these fits we have obtained the N2- broadening and narrowing coefficients of C2H2 and examined their temperature dependence. The experimentally measured narrowing coefficients have been used to estimate the nitrogen diffusion coefficients (D12) and are presented within. The broadening coefficients and corresponding temperature dependence exponents have also been compared to that of calculations completed using a classical impact approach on an ab initio potential energy surface. We have observed a good agreement between our theoretical and experimental results. Utilisant un spectromètre à diode laser à trois canaux, nous avons enregistré six transitions dans l'acétylène perturbée par de l'azote à l'intérieur de la bande d'absorption ν1 + ν3. Le but est d'améliorer notre compréhension des mécanismes d'élargissement et de resserrement dans l'acétylène à basse pression en présence d'azote. À cette fin, nous avons étudié les spectres de C2H2 en utilisant un profil de Rautian de collisions dures pour cinq températures dans le domaine 213-333 K et cinq pressions dans le domaine 5-40 Torr. À partir ce ces ajustements numériques, nous avons obtenu les coefficients d'élargissement et de resserrement de C2H2 et avons examiné leur dépendance en température. Nous avons utilisé les valeurs obtenues expérimentalement pour les coefficients de resserrement afin d'estimer les coefficients de diffusion de l'azote (D12) et nous les présentons ici. Les coefficients d'élargissement et la dépendance en température sont aussi comparés aux résultats de calculs qui utilisent une approche de collisions classiques et une surface d'énergie potentielle obtenue de principes premiers. Nous observons un bon accord entre calculs théoriques et valeurs expérimentales

High resolution spectroscopy and applications

xlii, 221 leaves : ill. ; 29 cmWith the ever increasing spectral resolution now achievable with modern spectrometers we do not just observe dark lines anymore but molecular absorption features at very high resolution. These features are governed by the kinematics of the molecules and can be examined carefully by using high resolution spectroscopy. A detailed description of the setup and performance of the tunable diode laser spectrometer (TDL) system used in my research is presented. This tunable laser system has been used to complete several high resolution line shape studies on the 1+ 2+ 4+ 5 and 1+ 3 combination bands of acetylene. The major focus of the presented results has been on the temperature dependence of the retrieved parameters and the identification of the best fitting line shape profile used in the present investigation. Improved spectral resolution also requires better understanding of its effects on the recorded data that could not have been observed on data obtained with low resolution instruments. One of these effects is known as line mixing and it occurs when neighbouring transitions interfere with each other causing a slight asymmetry in the spectral profile. In this Thesis I have examined the line mixing effect in CO2 spectra and the temperature dependence of these line mixing coefficients. The analysis is performed by using two common line mixing models; (1) the energy correct sudden approximation and (2) the exponential power gap law. Finally I will present a project based on the application of high resolution spectroscopy that involves monitoring N2O concentration at remote locations through the use of a long path gas cell and a tunable diode laser spectrometer system. The initial testing and setup of this monitoring system will be presented and discusse

Low-pressure line shape study of acetylene transitions in the v1 + v2 + v4 + v5 band over a range of temperatures

In this study we have retrieved the self-broadened widths, self-pressure-induced shifts, and Dicke narrowing coefficients for 20 R-branch transitions in the v1+v2+v4+v5 band of acetylene. The spectra were recorded using a three-channel diode laser spectrometer, a temperature-controlled cell of fixed length and a second, room temperature cell. The soft collision (Galatry) and hard collision (Rautian) profiles with inclusion of line mixing effects were used to retrieve the line parameters. We determined the temperature dependencies for line broadening, shift, and Dicke narrowing coefficients. We performed comparisons between our retrieved line parameters and published line parameters for acetylene transitions. © 2012 Taylor and Francis.SCOPUS: cp.jinfo:eu-repo/semantics/publishe

Line shape study of acetylene transitions in the ν1 + ν2 + ν4 + ν5 band over a range of temperatures

In this study we have retrieved the line intensities, self broadened widths, pressure-induced shifts and selected line mixing coefficients for 20 R-branch transitions in the ν1 + ν2 + ν4 + ν5 band of acetylene. The spectra were recorded using our 3-channels diode laser spectrometer, a temperature controlled cell of fixed length and a second, room temperature cell. The Voigt and speed-dependent Voigt profiles with inclusion of line mixing effects were used to retrieve the line parameters. We determined the temperature dependencies for line broadening, shift and line mixing coefficients. © 2011 Elsevier Inc. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Room Temperature Self- and H 2 -Broadened Line Parameters of Carbon Monoxide in the First Overtone Band: Theoretical and Revised Experimental Results

International audienceLorentz self- and H2-broadened half-width and pressure-induced shift coefficients, line mixing coefficients as well as line center positions and intensities were obtained using a nonlinear least square fitting technique for 48 (P(24) to R(23)) ro-vibrational transitions belonging to the first overtone (2←0) band of 12C16O at room temperature. All spectra in the 4146 to 4332 cm−1 spectral interval were fitted simultaneously employing four line shape functions: the Voigt, Speed Dependent Voigt, Rautian and Speed Dependent Rautian profiles. The collisional line mixing effect has been observed and investigated as an asymmetry in the analyzed line profiles. A semi-empirical Exponential Power Gap Law method was used to estimate the self- and H2-broadening coefficients and the collisional line mixing parameters. Additionally, a classical approach was applied to calculate the half-width coefficients of transitions in the 2←0 band for carbon monoxide broadened by H2 and for pure CO. The classical approach based on a simple computational method, ensures the molecular motion is correctly characterized in 3 dimensions. The calculations used vibrationally independent intermolecular interaction potentials. The variation of CO half-width coefficients with rotational quantum number J ≤ 24 was computed and compared with measurements. The agreement between the theoretical broadening coefficients is better for pure CO rather than for the CO-H2 system

Spectroscopic lineshape study of the self-perturbed oxygen A-band

This paper reports accurate line positions, intensities, self-broadening, -shift and -line mixing coefficients for 56 rotational transitions from multispectrum fits of low noise, high-resolution Fourier-transform spectra. The measured line intensities are within the statistical spread of the previous measurements available in the literature-thus contributing to the efforts to measure the oxygen A-band intensities with an accuracy better than 1%. We determined the integrated band strength and Einstein A coefficient. Using our spectrum calibration method we could clearly show for the first time that there is a meaningful statistical discrepancy in the frequency standards used in spectroscopic studies for the oxygen A-band. We were able to explain how this discrepancy leads to two different sets of shifts reported in the literature and demonstrate the need for precise frequency-type transition wavenumber measurements of the oxygen A-band transitions. We observed deviations from the conventional Voigt profile due to speed-dependent broadening and line mixing effects. Dicke narrowing was observed on a selected group of spectra recorded at pressures between 98 and 337 Torr. The Dicke narrowed lineshapes were best modeled using a Galatry profile implemented using a fixed value for the velocity-changing collision rate. The weak line mixing coefficients were determined from fits using the speed-dependent models. Exponential Power Gap (EPG) and Energy Corrected Sudden (ECS) scaling laws were used to calculate the self-broadening and self-line mixing coefficients. © 2007 Elsevier Inc. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Recent Line-Shape and Doppler Thermometry Studies Involving Transitions in the ν₁ +ν₃ Band of Acetylene

<p>The line positions for transitions in the <em>ν</em>₁+<em>ν</em>₃band are often used as a frequency standard by the telecom industry and also needed for planetary atmospheric studies. Four relevant studies have been recently carried out in our group and will be discussed briefly below. (1) <em>N</em>₂-broadened line widths and <em>N</em>₂-pressure induced line shifts have been measured for transitions in the <em>ν</em>₁+<em>ν</em>₃band of acetylene at seven temperatures in the range 213333K to obtain the temperature dependences of broadening and shift coefficients. The Voigt and hard-collision line profile models were used to retrieve the line parameters. This study has been published in Molecular Physics, 110 Issue 21/22 (2012) 2645-2663. (2) Six nitrogen perturbed transitions of acetylene within the <em>ν</em>₁+<em>ν</em>₃absorption band have been recorded using a 3-channel diode laser spectrometer. We have examined <em>C</em>₂<em>H</em>₂spectra using a hard collision (Rautian) profile over a range of five temperatures (213 K-333 K). From these fits we have obtained the <em>N</em>₂-broadening and narrowing coefficients of <em>C</em>₂<em>H</em>₂and examined their temperature dependence. The experimentally measured narrowing coefficients have been used to estimate the nitrogen diffusion coefficients. The broadening coefficients and corresponding temperature dependence exponents have also been compared to that of calculations completed using a classical impact approach on an ab initio potential energy surface. We have observed a good agreement between our theoretical and experimental results. This study was published in Canadian Journal of Physics 91(11) 896-905 (2013). (3) An extension of the previous study was to analyze the room temperature for the same six transitions using the Voigt, Rautian, Galatry, RautianGalatry and Correlated Rautian profiles. For the entire pressure range, we have tested the applicability of these line-shape models. Except for Voigt profile, Dicke narrowing effect has been considered in all mentioned line-shape models. The experimental results for the narrowing parameters have been compared with calculated values based on the theory of diffusion. This study is in press in press in the Journal of Quantitative Spectroscopy and Radiative Transfer. (4) In this paper we present accurate measurements of the fundamental Boltzmann constant based on a lineshape analysis of acetylene spectra in the <em>ν</em>₁+<em>ν</em>₃band recorded using a tunable diode laser. Experimental spectra recorded at low pressures have been analyzed using both the Voigt model and the Speed Dependent Voigt model that takes into account the molecular speed dependence effects. These line-shape models reproduces the experimental data with high accuracy and allow us to determine precise line-shape parameters for the transitions used, the Doppler-width and then determined the Boltzmann constant, <em>k</em><em>_B</em>. This study has been submitted for publication in the Journal of Chemical Physics. ¹</p> <p> </p> <p> </p> <p>1 Research described in this work was funded by NSERC, Canada.</p

Corrigendum to "Measurement and computations for temperature dependences of self-broadened carbon dioxide transitions in the 30012-00001 and 30013-00001 bands" [J. Quant. Spectrosc. Radiat. Transf. 111 (9) (2010) 1065-1079] doi: 10.1016/j.jqsrt.2010.01.003

SCOPUS: er.jinfo:eu-repo/semantics/publishe

Corrigendum to "Measurement and computations for temperature dependences of self-broadened carbon dioxide transitions in the 30012-00001 and 30013-00001 bands" [J. Quant. Spectrosc. Radiat. Transf., 111 (9) (2010) 1065-1079] doi: 10.1016/j.jqsrt.2010.01.003

Peer reviewed: YesNRC publication: Ye