Line profile study of transitions in the 30012 ← 00001 and 30013 ← 00001 bands of carbon dioxide perturbed by air

In this work we present a line profile study for air-broadened carbon dioxide transitions in the 30012 ← 00001 and 30013 ← 00001 vibrational bands. The room temperature spectra were recorded at a resolution of 0.008 cm⁻¹ using a Fourier Transform spectrometer. The air-broadening, air-shift, and air-line mixing coefficients were derived from a simultaneous fitting of spectra using the Voigt model and a Speed-Dependent Voigt lineshape model. The results obtained are consistent with other studies in addition to the theoretically calculated values. Exponential Power Gap (EPG) and Energy Corrected Sudden (ECS) scaling laws were used to calculate the relaxation matrix elements.     

Measurement and computations for temperature dependences of self-broadened carbon dioxide transitions in the 30012←00001 and 30013←00001 bands

Using a Fourier transform spectrometer setup we have measured the self-broadened half width, pressure shift, and line asymmetry coefficients for transitions in the 30012←00001 and 30013←00001 vibrational bands of carbon dioxide for four different temperatures. A total of 46 pure CO₂ spectra were recorded at 0.008 and 0.009 cm⁻¹ resolution and at pressures varying from a few Torr to nearly an atmosphere. The individual spectral line profiles have been fitted by a Voigt profile and a speed-dependent Voigt profile, to which we have added dispersion profiles to account for weak line mixing. A comparison of the sets of results obtained for each band showed no vibrational dependence of the broadening coefficients. The self-broadening and self-shift coefficients are compared to semiclassical calculations based on the Robert-Bonamy formalism and were found to be in good agreement. The line asymmetry results are compared to line mixing calculations based on the Energy Corrected Sudden (ECS) and Exponential Power Gap models.     

Line mixing and speed dependence in CO2 at 6227.9 cm: Constrained multispectrum analysis of intensities and line shapes in the 30013 ← 00001 band

Line position, intensity and line shape parameters (Lorentz widths, pressure shifts, line mixing, speed dependence) are reported for transitions of the 30013 ← 00001 band of ¹⁶O¹²C¹⁶O (ν₀ = 6227.9 cm⁻¹). The results are determined from 26 high-resolution, high signal-to-noise ratio spectra recorded at room temperature with the McMath-Pierce Fourier transform spectrometer. To minimize the systematic errors of the retrieved parameters, we constrained the multispectrum nonlinear least squares retrieval technique to use quantum mechanical expressions for the rovibrational energies and intensities rather than retrieving the individual positions and intensities line by line. Self- and air-broadened Lorentz width and pressure-induced shift, speed dependence and line mixing (off-diagonal relaxation matrix elements) coefficients were adjusted individually. Errors were further reduced by simultaneously fitting the interfering absorptions from the weak 30012 ← 00001 band of ¹⁶O¹³C¹⁶O as well as the weak hot bands 31113 ← 01101, 32213 ← 02201, 40014 ← 10002 and 40013 ← 10001 of ¹⁶O¹²C¹⁶O in this spectral window. This study complements our previous work on line mixing and speed dependence in the 30012 ← 00001 band (ν₀ = 6347.8 cm⁻¹) [V.M. Devi, D.C. Benner, L.R. Brown, C.E. Miller, R.A. Toth, J. Mol. Spectrosc. 242 (2007) 90-117] and provides key data needed to improve atmospheric remote sensing of CO₂.     

Lineshape analysis of the J = 3 ← 2 and J = 5 ← 4 rotational transitions of room temperature CO broadened by N2, O2, CO2 and noble gases

Collisional relaxation has been considered for millimeter lines of carbon monoxide at room temperature. Accurate measurements of carbon dioxide- and rare gases-broadened widths have been performed on the J = 3 ← 2 rotational line of ¹²CO by using a video-type spectrometer. Measurements of nitrogen-, oxygen-, and xenon-broadened widths of the J = 5 ← 4 rotational line of ¹³CO were also carried by using a frequency-modulated spectrometer. A lineshape study performed on all the investigated binary systems provide confirmation that Voigt profile is not a suitable model to analyse experimental lines in the millimeter-waves region. On one hand, using this profile in the low pressure range, i.e. in the Doppler regime, the retrieved collisional linewidths do not follow a linear variation with the perturbing gas pressure. On the other hand, regardless of the pressure, lineshapes exhibit a narrowed profile. An accurate analysis of the pressure dependence of relaxation rates show that the Galatry profile is not appropriate and that experimental lineshapes are actually Speed Dependent Voigt profiles. Accurate broadening parameters were retrieved from this profile and compared to previous reported values and predictions calculated from the Robert-Bonamy formalism. Finally a variation of the ratio of relaxation speed dependence to broadening parameters versus relative masses of the collision partners is presented.     

Air-broadened halfwidth and pressure shift coefficients of CO2 bands: 4750-7000 cm

Previously we obtained self-broadened halfwidth and self-induced shift coefficients at room temperature for 15 near infrared CO₂ bands between 4750 and 7000 cm⁻¹ [R.A. Toth, L.R. Brown, C.E. Miller, V.M. Devi, D.C. Benner, J. Mol. Spectrosc., 239 (2006) 243-271]. The present study expands our work on the near infrared line parameters of CO₂ to include air broadening coefficients. Here we report nearly 400 air-broadened half width and air-induced pressure shift coefficients spanning 11 different CO₂ vibrational bands in the 4750-7000 cm⁻¹ region. Retrievals have been performed using Voigt line profiles over three distinct spectral intervals: (a) 4750-5200 cm⁻¹, covering the 20011 ← 00001, 20012 ← 00001, and 20013 ← 00001 Fermi Triad and three associated hot bands 21111 ← 01101, 21112 ← 01101, 21113 ← 01101; (b) 6100-7000 cm⁻¹, covering the 30011 ← 00001, 30012 ← 00001, 30013 ← 00001 and 30014 ← 00001 Fermi Tetrad; (c) near 6950 cm⁻¹ for the 00031 ← 00001 overtone band. The air-broadened halfwidth and air-induced pressure shift coefficients have been modeled with empirical expressions and compared to other measurements available in the literature.     

N2-, H2-, and He-induced collisional broadening of the J = 24 ← 23 transition of HC3N located near 218.3 GHz at different temperatures

We report on experimental collisional relaxation of the J = 24 ← 23 line of HC₃¹⁴N, located near 218.3 GHz, induced by nitrogen, hydrogen, and helium. The measurements were carried out at selected temperatures in the 235-350 K range using a video-type spectrometer. The foreign gas broadening parameters and their temperature dependences were determined assuming Voigt lineshape profiles and the usual T⁻ⁿ temperature law. The experimental broadening parameters are compared with results derived using the ATC collisional formalism.     

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.     

Pressure-induced line broadening for the (30012)←(00001) band of CO2 measured with tunable diode laser photoacoustic spectroscopy

Pressure-induced foreign-broadening lineshape parameters of the carbon dioxide rovibrational transitions belonging to the (30012)←(00001) overtone band near the 1.573 μm wavelength region are measured by using a tunable diode laser photoacoustic spectrometer. The spectroscopic analysis has concerned the first 11 lines of the R branch. For these lines, the air- and Ar-broadening coefficients are measured at room temperature (∼298 K). The measured broadening coefficients of all the transitions of ¹²C¹⁶O₂ are compared with those given in the HITRAN04 database and former measurements with a different spectroscopic method. Agreements and discrepancies are underlined and briefly discussed. The recorded lineshapes are fitted with standard Voigt line profiles in order to determine the collisional broadening coefficient of carbon dioxide transitions.     

Self-broadened widths and shifts of CO2: 4750-7000 cm

In the previous paper, we report line strength measurements for 58 bands of ¹²CO₂ between 4550 and 7000 cm⁻¹ [R.A. Toth, L.R. Brown, C.E. Miller, V. Malathy Devi, D. Chris Benner, J. Mol. Spectrosc., this issue, doi:10.1016/j.jms.2006.008.001.]. In the present study, self-broadenedwidth and self-induced pressure shift coefficients are determined in two intervals:

(a) between 4750 and 5400 cm⁻¹for bands of the Fermi triad (20011 ← 00001, 20012 ← 00001, 20013 ← 00001), three corresponding hot bands (21111 ← 01101, 21112 ← 01101, 21113 ← 01101) and the 01121← 00001 combination band;

(b) between 6100 and 7000 cm⁻¹ for the Fermi tetrad (30014 ← 00001, 30013 ← 00001, 30012 ← 00001, 30011 ← 00001), two associated hot bands (31113 ← 01101, 31112 ← 01101), as well as 00031 ← 00001 and its hot band 01131 ← 01101.

Least-squares fits of the experimental width and pressure shift coefficients are modeled using empirical expressions:

     

Line mixing and speed dependence in CO2 at 6348 cm: Positions, intensities, and air- and self-broadening derived with constrained multispectrum analysis

Intensity and line shape parameters which predict spectral lines with absolute accuracies better than 0.3% have been determined for transitions of the 30012 ← 00001 band of ¹⁶O¹²C¹⁶O centered near 6348 cm⁻¹ from 26 high resolution, high signal-to-noise ratio spectra recorded at room temperature with the McMath-Pierce Fourier transform spectrometer. To maximize the accuracies of the retrieved parameters, the multispectrum non-linear least squares retrieval technique was modified to adjust the rovibrational constants (G, B, D, etc.) and intensity parameters, including Herman-Wallis terms, rather than retrieving the individual positions and intensities. Speed-dependent Voigt line shapes with line mixing were required to remove systematic errors in the fit residuals. Self- and air-broadening (widths and pressure-induced shifts, speed dependence parameters) and line mixing (off-diagonal relaxation matrix elements) coefficients were thus obtained in the multispectrum fit. Remaining errors were minimized by fitting the weak 30011 ← 00001 band of ¹⁶O¹³C¹⁶O as well as the weak hot bands 31112 ← 01101, 32212 ← 02201, 40012 ← 10001, and 40013 ← 10002 of ¹⁶O¹²C¹⁶O that contribute interfering absorptions in this spectral window. This study presents the most extensive set of measurements to date for self- and air-broadening and self- and air-shift coefficients of a near infrared band of CO₂. This is also the first study where line mixing parameters have been experimentally determined for any parallel CO₂ band.     

Broadening, shifting, and line mixing in the 030 ← 010 parallel Q branch of N2O

The 03¹0 ← 01¹0 parallel Q branch of N₂O has been studied at 297 K and over the pressure range 1-130 torr. Absorption spectra were recorded using a high resolution (1.5 MHz or 5 × 10⁻⁵ cm⁻¹) and high signal-to-noise (>3500:1) mid-infrared spectrometer based on difference-frequency infrared generation in AgGaS₂. In the low-pressure range (1-11 torr) we obtained accurate values for the line strengths, the broadening coefficients, the weak mixing coefficients, and the overall shifting of the branch. The medium pressure results, ranging from 23 to 130 torr, were analyzed by treating the band as a whole, using a relaxation matrix formalism, based on an energy gap scaling law. We find, effectively, that only 36% of the rotationally inelastic collisions are associated with Q branch mixing, the rest presumably being associated with Q-P and Q-R mixing in the same vibrational band. The pressure shifting coefficient of the 03¹0 ← 01¹0 Q branch as a whole was also determined and found to be 5.8 × 10⁻³ cm⁻¹/atm towards lower frequencies.     

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.     

Self-broadened CO line shapes in the v=2←0 band

Precise intensities, self-broadenings and shifts have been obtained for the ¹²C¹⁶O v=2←0 band from simultaneous fits of low-noise, high-resolution Fourier-transform spectra at pressures from 27 to 80 kPa (200-600 Torr). Observed line shapes exhibit deviations on the order of 1% from the conventional Voigt profile, primarily due to speed-dependent broadening and secondarily to line mixing. Dicke narrowing is reduced by over an order-of-magnitude from the diffusion value, presumably because of correlations between velocity- and phase-changing collisions.     

The Lamb-dip spectrum of the J = 1 ← 0 transition of DF: Crossing resonances and hyperfine components

The Lamb-dip technique has been applied to the observation of the J = 1 ← 0 transition of DF: for the first time, the hyperfine structure due to D and F have been resolved by using microwave spectroscopy. The high accuracy of this technique allows us to provide hyperfine parameters that are in very good agreement with those obtained from molecular beam experiment. In addition, our frequencies together with the unresolved ones up to J″ value of 47 allow us to provide the most accurate ground state rotational constants of DF known at the moment. Furthermore, due to the presence of a relevant number of strong crossing resonances, the J = 1 ← 0 transition of DF can be considered an illustrative case to show how they modify the shape of Lamb-dip spectra.     

Spectral line parameters in the (3 ← 0) overtone band of the HI molecule and line-mixing in the band head

The linestrengths, self-pressure broadening and shifting coefficients have been measured for P₃ (10)- R₃ (12) lines in the second overtone band of hydrogen iodide. A dipole moment function in terms of the reduced nuclear displacement x = (R − R_e)/R_e is obtained using rotationless dipole matrix elements determined by the Herman-Wallis analysis of the (1, 2, 3 ← 0) HI bands: μ (x) = 0.4471(5) − 0.0770(2)x + 0.547(3)x² − 1.93(2)x³, in a full agreement with the function proposed previously [J. Mol. Spectrosc. 223 (2004) 67]. A close match is demonstrated of the results of most recent relativistic calculations [Phys. Chem. Chem. Phys. 6 (2004) 3779] with the spectroscopically derived electric dipole parameters for HI. Line-mixing in the band head is observed, the self-pressure shifting and broadening coefficients for the (3 ← 0) band lines are determined.     

Self- and H2-broadened width and shift coefficients in the 2 ← 0 band of CO: revisited

Room temperature values for self-broadened and hydrogen-broadened Lorentz halfwidth coefficients, and self and hydrogen pressure-induced shift coefficients have been measured for transitions with rotational quantum number m ranging between −24 and 24 in the 2 ← 0 band of ¹²C¹⁶O. The spectra were recorded with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak. The analysis was performed using a multispectrum nonlinear least squares technique. We have compared our results with similar measurements published recently.     

Line positions and strengths of OCO, OCO and OCO between 2200 and 7000 cm

Line positions and strengths of ¹⁶O¹²C¹⁸O (628), ¹⁸O¹²C¹⁸O (828) and ¹⁷O¹²C¹⁸O (728) were measured between 2200 and 7000 cm⁻¹ using 22 near infrared (NIR) absorption spectra recorded at 0.01-0.013 cm⁻¹ resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. These data were obtained at room temperature using absorption cells with optical path lengths ranging from 2.4 to 385 m; the cells were filled with natural and ¹⁸O-enriched samples of CO₂ at pressures ranging from 0.54 to 252 torr. The observed line positions were analyzed to obtain the upper state band centers and rotational constants for 17 bands of ¹⁶O¹²C¹⁸O, 19 bands of ¹⁸O¹²C¹⁸O and 8 bands of ¹⁷O¹²C¹⁸O. The majority of the ¹⁸O¹²C¹⁸O and ¹⁷O¹²C¹⁸O bands were measured for the first time. In addition, the rotational constants for the lower states 00001, 01101e and 01101f were derived for all three species using the method of combination differences in which the averaged values obtained from the line positions of two or more bands were least-squares-fitted. Rovibrational parameters were also obtained for the 02201e, 02201f, 10002 and 10001 states of ¹⁸O¹²C¹⁸O. The line position analysis revealed that transitions of the levels 38 ? J′ ? 46 of the 11111f ← 01101f band of ¹⁸O¹²C¹⁸O are perturbed. Perturbed transitions were also observed for the 12212 ← 02201 band and in the high-J transitions (J′ ? 49) of the 20012 ← 00001 band of ¹⁸O¹²C¹⁸O. Band strengths and Herman-Wallis-like F-factor coefficients were determined for 21 bands of ¹⁶O¹²C¹⁸O, 25 bands of ¹⁸O¹²C¹⁸O and 8 bands of ¹⁷O¹²C¹⁸O from least-squares fits to more than 3700 measured transition intensities; band strengths and line positions for 34 of these bands were obtained for the first time.     

Line strengths of CO2: 4550-7000 cm

Line positions and strengths of ¹²C¹⁶O₂ were measured between 4550 and 7000 cm⁻¹ using near infrared absorption spectra recorded at 0.01-0.013 cm⁻¹ resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory at Kitt Peak, Arizona. These were retrieved from 42 laboratory spectra obtained at room temperature with five absorption cells having various optical path lengths (from 0.1 to 409 m) filled with natural and enriched samples of CO₂ at pressures ranging from 2 to 581 Torr. In all, band strengths and Herman-Wallis-like F-factor coefficients were determined for 58 vibration-rotation bands from the least-squares fits of over 2100 unblended line strengths; strengths of 34 of these bands had not been previously reported. Band strengths in natural abundance generally ranged from 3.30 × 10⁻²⁰ to 2.8 × 10⁻²⁵ cm⁻¹/molecule cm⁻² at 296 K. It was found that the high J transitions (J′ ? 61) of the 20012 ← 00001 band centered at 4977.8347 cm⁻¹ are perturbed, affecting both measured positions and strengths. Two other interacting bands, 21113e ← 01101e and 40002e ← 01101e, were also analyzed using degenerate perturbation theory. Comparisons with corresponding values from the literature indicate that absolute accuracies better than 1% and precisions of 0.5% were achieved for the strongest bands.     

Diode laser spectroscopic measurements and theoretical calculations of line parameters of nitrogen-broadened water vapor overtone transitions in the 818-834 nm wavelength region

Nitrogen-broadened water vapor line parameters of the (2 1 1) ← (0 0 0) overtone band transitions in the 818-834 nm wavelength region are measured by using a tunable diode laser spectrometer. Water vapor is kept at its saturated vapor pressure at room temperature within a sample cell. Use of a balanced detector and a lock-in amplifier helps to increase the detection efficiency and the signal-to-noise ratio. The collisional broadening coefficients are extracted from the fitting of the experimental data by using a standard Voigt line profile. Collisional half-widths of water vapor lines perturbed by nitrogen are evaluated using the complex-valued implementation of the Robert-Bonamy (CRB) formalism. The rotational wave functions and the energy eigenvalues in the (2 1 1) vibrational state of water molecule are assumed on the basis of symmetry properties. Hence the outcome of this work also tests the validity of the theoretical approximations. The experimental data are compared with the corresponding theoretical values and the possible causes of deviation between the two have also been discussed.     

Rotational levels of the (0 0 0) and (0 1 0) states of D2O from hot emission spectra in the 320-860 cm region

The far-infrared emission spectra of deuterated water vapour were measured at different temperatures (1370, 1520, and 1950 K) in the range 320-860 cm⁻¹ at a resolution of 0.0055 cm⁻¹. The measurements were performed in an alumina cell with an effective length of hot gas of about 50 cm. More than 1150 new measured lines for the D₂¹⁶O molecule corresponding to transitions between highly excited rotational levels of the (0 0 0) and (0 1 0) vibrational states are reported. These new lines correspond to rotational states with higher values of the rotational quantum numbers compared to previously published determinations: J_max=26 and for the (0 0 0) ← (0 0 0) band, J_max=25 and for the (0 1 0) ← (0 1 0) band, and J_max=26 and for the (0 1 0) ← (0 0 0) band. The estimated accuracy of the measured line positions is 0.0005 cm⁻¹. To our knowledge no experimentally measured rotational transitions for D₂¹⁶O within an excited vibrational state have been available in the literature so far. An extended set of experimental rotational energy levels for (0 0 0) and (0 1 0) vibration states including all previously available data has been determined. For the data reduction we used the generating function model. The root mean square (RMS) deviation between observed and calculated values is 0.0012 cm⁻¹ for 692 rotational levels of the (0 0 0) state and 0.0010 cm⁻¹ for 639 rotational levels of the (0 1 0) vibrational state. A comparison of the observed energy levels with the best available values from the literature and with the global predictions from molecular electronic potential energy surface [J. Chem. Phys. 106 (1997) 4618] for the (0 0 0) and (0 1 0) states is discussed.