Self-broadened Half-widths Research Articles

Development and validation of a laser-absorption-based method for in-situ and high-precision water vapor dew point temperature measurement

Dew point temperature is an important gas state parameter. Accurately measuring dew point temperature is a challenge because it is not only related to gas concentration, but also gas temperature and pressure. We proposed a dew point temperature measurement method based on tunable diode laser absorption spectroscopy (TDLAS), in which water vapor temperature, pressure and concentration can be measured simultaneously with a single near-infrared laser source. Two H2O absorption lines near 1381 nm (7242.37 cm−1 and 7243.08 cm−1) were selected, and their coefficients of temperature-dependence of the self-broadened half-width were measured experimentally to improve the HITRAN databases. The wavelength shift of the laser was suppressed by a temperature compensation circuit. To confirm the capability of this method, a series of experiments were performed in a standard temperature and humidity chamber through the target absorption lines. In the whole dew point range of the experiment, the maximum deviation between the measurement results of our method and the high precision chilled mirror hygrometer is less than 0.9 ℃. According to the time-series measurements of atmospheric H2O, the measurement accuracy of 0.57% and the detection limit of −61.1 ℃ were verified under the condition that the optical path was only 10.5 cm. This result shows the potential of this method in low-cost, calibration-free, in-situ and high-precision dew point measurement.

Addition of the line list for carbon disulfide to the HITRAN database: line positions, intensities, and half-widths of the 12C32S2, 32S12C34S, 32S12C33S, and 13C32S2 isotopologues

A new ro-vibrational line list for the 12C32S2, 32S12C34S, 32S12C33S, and 13C32S2 isotopologues of carbon disulfide, including line positions, intensities, and linewidths, has been produced as part of the HITRAN2020 project. The carbon disulfide line list covers the range from about 0 to 6470 cm−1 (1.55 µm). The calculations of the line positions and intensities were performed by applying the PGOPHER program using a large set of measured line positions available in the literature, including the most recent high-precision dual-comb laser spectroscopy measurements and transition dipole moments for each measured band. The bands which did not have available intensity measurements were scaled to the experimental cross-sections from the PNNL database. Semi-empirical models for rotational dependence of air- and self-broadened half widths are developed based on the available experimental data.A total of 94992 transitions corresponding to 423 cold and hot bands of the 12C32S2, 32S12C34S, 32S12C33S, and 13C32S2 isotopologues up to a maximum rotational angular momentum J=150 have been calculated. The CS2 line list has been generated in HITRAN format and is provided as supplementary material and will be a part of the next edition of the HITRAN database distributed through https://www.hitran.org. This list will be useful in the fields of atmospheric environmental chemistry, medical diagnostics and planetary atmospheres.

CDSD-296, high-resolution carbon dioxide spectroscopic databank: An update

In 2015 we published an atmospheric version, CDSD-296, of the carbon dioxide spectroscopic databank (CDSD) [Tashkun et al., JQSRT 152 (2015) 45–73]. Since that time many new experimental data have been published. Some CDSD data deficiencies have also been found. The purpose of the present work is to present a corrected and extended version of the databank. In particular, it includes more realistic uncertainties of the line positions and intensities. The databank contains the calculated line parameters (positions, intensities, air- and self-broadened half-widths and their coefficients of temperature dependence, as well as air- and self- pressure-induced shifts) of the twelve stable isotopic species of CO2. The reference temperature is 296 K, and the intensity cutoff is 10−30 cm−1/(molecule cm−2). More than 530,000 lines covering the 345–14,076 cm−1 spectral range are included in the databank. Comparisons of the new version of the CDSD with UCL, AMES and HITRAN2016 line lists are also given.

Relaxation matrix for symmetric tops with inversion symmetry: Line coupling and line mixing effects on NH3 lines in the 𝝂4 band.

Line shape parameters including the half-widths and the off-diagonal elements of the relaxation matrix have been calculated for self-broadened NH3 lines in the perpendicular ν4 band. As in the pure rotational and the parallel ν1 bands, the small inversion splitting in this band causes a complete failure of the isolated line approximation. As a result, one has to use formalisms not relying on this approximation. However, due to differences between parallel and perpendicular bands of NH3, the applicability of the formalism used in our previous studies of the ν1 band and other parallel bands must be carefully verified. We have found that, as long as potential models only contain components with K1 = K2 = 0, whose matrix elements require the selection rule Δk = 0, the formalism is applicable for the ν4 band with some minor adjustments. Based on both theoretical considerations and results from numerical calculations, the non-diagonality of the relaxation matrices in all the PP, RP, PQ, RQ, PR, and RR branches is discussed. Theoretically calculated self-broadened half-widths are compared with measurements and the values listed in HITRAN 2012. With respect to line coupling effects, we have compared our calculated intra-doublet off-diagonal elements of the relaxation matrix with reliable measurements carried out in the PP branch where the spectral environment is favorable. The agreement is rather good since our results do well reproduce the observed k and j dependences of these elements, thus validating our formalism.

Vibrational dependence of line coupling and line mixing in self-broadened parallel bands of NH3

Line coupling and line mixing effects have been calculated for several self-broadened NH3 lines in parallel bands involving an excited ν2 mode. It is well known that once the ν2 mode is excited, the inversion splitting quickly increases as this quantum number increases. In the present study, we have shown that the ν2 dependence of the inversion splitting plays a dominant role in the calculated line-shape parameters. For the ν2 band with a 36cm−1 splitting, the intra-doublet couplings practically disappear and for the 2ν2 and 2ν2 - ν2 bands with much higher splitting values, they are completely absent. With respect to the inter-doublet coupling, it becomes the most efficient coupling mechanism for the ν2 band, but it is also completely absent for bands with higher ν2 quantum numbers. Because line mixing is caused by line coupling, the above conclusions on line coupling are also applicable for line mixing. Concerning the check of our calculated line mixing effects, while the present formalism has well explained the line mixing signatures observed in the ν1 band, there are large discrepancies between the measured Rosenkranz mixing parameters and our calculated results for the ν2 and 2ν2 bands. In order to clarify these discrepancies, we propose to make some new measurements. In addition, we have calculated self-broadened half-widths in the ν2 and 2ν2 bands and made comparisons with several measurements and with the values listed in HITRAN 2012. In general, the agreements with measurements are very good. In contrast, the agreement with HITRAN 2012 is poor, indicating that the empirical formula used to predict the HITRAN 2012 data has to be updated.

NOSD-1000, the high-temperature nitrous oxide spectroscopic databank

We present a high-temperature version, NOSD-1000, of the nitrous oxide spectroscopic databank. The databank contains the line parameters (positions, intensities, air- and self-broadened half-widths and coefficients of temperature dependence of air- and self-broadened half-widths) of the most abundant isotopologue 14N216O of the nitrous oxide molecule. The reference temperature is Tref=1000K and the intensity cutoff is Icut=10−25cm−1/(molecule cm−2). More than 1.4 million lines covering the 260–8310cm−1 spectral range are included in NOSD-1000. The databank has been generated within the framework of the method of effective operators and based on the global fittings of spectroscopic parameters (parameters of the effective Hamiltonian and effective dipole moment operators) to observed data collected from the literature. Line-by-line simulation of a medium-resolution high-temperature (T=873K) spectrum has been performed in order to validate the databank. NOSD-1000 is freely accessible via the Internet.

CDSD-296, high resolution carbon dioxide spectroscopic databank: Version for atmospheric applications

We present an atmospheric version, CDSD-296, of the carbon dioxide spectroscopic databank (CDSD). The databank contains the calculated line parameters (positions, intensities, air- and self-broadened half-widths, coefficients of temperature dependence of air-broadened half-widths and air pressure-induced line shifts) of the twelve stable isotopic species of CO2. The reference temperature is Tref=296K and the intensity cutoff is Icut=10−30cm−1/(moleculecm−2). More than 500,000 lines covering the 6–14,075cm−1 spectral range are included in CDSD-296. The databank has been generated within the framework of the method of effective operators and based on the global weighted fits of spectroscopic parameters (parameters of the effective Hamiltonians and effective dipole moment operators) to observed data collected from the literature. The fitted models are able to reproduce known measured positions and intensities with accuracies compatible with measurement uncertainties. The line-shape parameters originate from the recent theoretical and semi-empirical calculations. Comparisons of CDSD-296 with HITRAN-2012, GEISA-2011, and the AMES line lists are also given.

Air- and self-broadened half widths, pressure-induced shifts, and line mixing in the ν2 band of 12CH4

Lorentz self- and air-broadened half width and pressure-induced shift coefficients and their dependences on temperature have been measured from laboratory absorption spectra for nearly 130 transitions in the ν2 band of 12CH4. In addition line mixing coefficients (using the relaxation matrix element formalism) for both self- and air-broadening were experimentally determined for the first time for a small number of transitions in this band. Accurate line positions and absolute line intensities were also determined. These parameters were obtained by analyzing high-resolution (~0.003 to 0.01cm−1) laboratory spectra of high-purity natural CH4 and air-broadened CH4 recorded at temperatures between 226 and 297K using the McMath–Pierce Fourier transform spectrometer (FTS) located at the National Solar Observatory on Kitt Peak, Arizona. A multispectrum nonlinear least squares technique was used to fit short (5–15cm−1) spectral intervals in 24–29 spectra simultaneously. Parameters were determined for ν2 transitions up to J″=16. The variations of the measured broadening and shift parameters with the rotational quantum number index and tetrahedral symmetry species are examined. The present results are also compared with previous measurements available in the literature.

CDSD-4000: High-resolution, high-temperature carbon dioxide spectroscopic databank

We present a high-resolution, high-temperature version of the Carbon Dioxide Spectroscopic Databank called CDSD-4000. The databank contains the line parameters (positions, intensities, air- and self-broadened half-widths, coefficients of temperature dependence of air- and self-broadened half-widths, and air-broadened pressure shifts) of the four most abundant isotopologues of CO 2. A reference temperature is 296 K and an intensity cutoff is 10 −27 cm −1/molecule cm −2 at 4000 K. The databank has 628,324,454 entries, covers the 226–8310 cm −1 spectral range and designed for the temperature range 2500–5000 K. Format of CDSD-4000 is similar to that of HITRAN-2008. The databank has been generated within the framework of the method of effective operators and based on the global fittings of spectroscopic parameters (parameters of the effective Hamiltonians and effective dipole moment operators) to observed data collected from the literature. The databank is useful for studying high-temperature radiative properties of CO 2, including exoplanets atmospheres, aerothemal modeling for Mars entry missions, high-temperature laboratory spectra, and industrial applications. CDSD-4000 is freely accessible via the Internet site ftp://ftp.iao.ru/pub/CDSD-4000.

A multispectrum analysis of the ν 4 band of 13CH 4: Widths, shifts, and line mixing coefficients

Line positions, Lorentz air-broadened half width and air pressure-induced shift coefficients have been measured for nearly 200 transitions in the ν 4 band of 13CH 4 from high-resolution spectra recorded with the McMath-Pierce Fourier transform spectrometer. Three room temperature spectra of 13CH 4 used in the previous study of Malathy Devi et al. (Air-broadened Lorentz halfwidths and pressure-induced line shifts in the ν 4 band of 13CH 4. Appl. Opt. 1988; 27: 2296–2308) were analyzed together with a large number of additional spectra of self- and air-broadened CH 4 recorded at 210–314 K and one room-temperature spectrum of self-broadened 13CH 4. Analyses applying the multispectrum nonlinear least squares fitting technique were performed to retrieve the spectral line parameters. In addition to air-broadened half width and shift coefficients, self-broadened half width and shift coefficients were determined for at least 56 13CH 4 ν 4 transitions. Off-diagonal relaxation matrix element coefficients for air-broadened line mixing were also determined for 28 pairs of P and R transitions in a number of J manifolds, and mixing parameters for self-broadening were also determined for some of these pairs. Temperature-dependences of the pressure-induced shift and mixing parameters for the 13CH 4 lines could not be determined from the spectra used in the present analysis, but temperature dependences of the half width coefficients were determined for the strongest transitions. The results of this study are compared with other studies of air- and self-broadened 13CH 4 and 12CH 4.

Multispectrum analysis of 12CH 4 in the ν 4 spectral region: II. Self-broadened half widths, pressure-induced shifts, temperature dependences and line mixing

Accurate values for line positions, absolute line intensities, self-broadened half width and self-pressure-induced shift coefficients have been measured for over 400 allowed and forbidden transitions in the ν 4 band of methane ( 12CH 4). Temperature dependences of half width and pressure-induced shift coefficients were also determined for many of these transitions. The spectra used in this study were recorded at temperatures between 210 and 314 K using the National Solar Observatory's 1 m Fourier transform spectrometer at the McMath-Pierce solar telescope. The complete data set included 60 high-resolution (0.006–0.01 cm −1) absorption spectra of pure methane and methane mixed with dry air. The analysis was performed using a multispectrum nonlinear least squares curve fitting technique where a number of spectra (20 or more) were fit simultaneously in spectral intervals 5–15 cm −1 wide. In addition to the line broadening and shift parameters, line mixing coefficients (using the off-diagonal relaxation matrix element formalism) were determined for more than 50 A-, E-, and F-species transition pairs in J manifolds of the P- and R-branches. The measured self-broadened half width and self-shift coefficients, their temperature dependences and the line mixing parameters are compared to self-broadening results available in the literature and to air-broadened parameters determined for these transitions from the same set of spectra.

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 CO 2 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.

Experimental intensity and lineshape parameters of the oxygen A-band using frequency-stabilized cavity ring-down spectroscopy

Line intensities, self- and air-broadened linewidths, pressure-induced shifts, and collisional narrowing coefficients were measured from 2 ⩽ J′ ⩽ 32 in the P branch of the O 2 A-band (12 975–13110 cm −1) utilizing Galatry line profiles. Spectra were recorded using the frequency-stabilized cavity ring-down spectrometer located at NIST, Gaithersburg, MD with a spectral resolution <0.0001 cm −1 and noise-equivalent absorption coefficient of 6 × 10 −8 m −1 Hz −1/2. Line intensities, obtained from calibrated gas samples for 2 ⩽ J′ ⩽ 32, are ∼1% lower than the values in current spectroscopic databases. At higher J (18 ⩽ J′ ⩽ 32), the measured air- and self- broadened half widths are up to 20% lower than the extrapolated values given in HITRAN 2004, while corresponding half-widths for 2 ⩽ J′ ⩽ 15 are in better agreement. Available self-broadened half widths are fitted to empirical expressions with an rms of 0.8%. We discuss the implications of our results for accurate remote sensing of surface pressure and photon path length distributions.

Air-broadened halfwidth and pressure shift coefficients of 12C 16O 2 bands: 4750–7000 cm −1

Previously we obtained self-broadened halfwidth and self-induced shift coefficients at room temperature for 15 near infrared CO 2 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 CO 2 to include air broadening coefficients. Here we report nearly 400 air-broadened half width and air-induced pressure shift coefficients spanning 11 different CO 2 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.

Self-broadened half-widths and self-induced line shifts for water vapor transitions in the 3.2–17.76 μm spectral region via complex Robert–Bonamy theory

Water vapor in the Earth’s atmosphere is being studied in the 3.2–17.76 μm spectral region by the atmospheric infrared sounder (AIRS) on Aqua, the troposphere emission spectrometer (TES) and the high-resolution dynamics limb sounder (HIRDLS) on Aura, both part of the NASA EOS mission. However, the lack of sufficient data on spectral parameters will hamper the prospect of accurate retrievals of temperature and concentration profiles. The spectral parameters for thousands of water vapor transitions are required, which are hard to determine by measurements alone. As reported previously [Can. J. Chem. 82 (2004) 1013–1027], of the 10 602 measurements of H 2O self-broadening half-widths only 440 intercomparisons with more than 3 data points have estimated uncertainty less than 10%. In this work, we have employed the mean relative thermal velocity approximation of the complex implementation of Robert–Bonamy formalism to obtain the self-broadened half-widths and self-induced line shifts for 5442 water vapor transitions in the 3.2–17.76 μm region. The calculations are compared with the measurement database and trends in the half-widths and line shifts are studied.

Self-broadening of water vapor transitions via the complex Robert–Bonamy theory

Calculations of self-broadened half-widths and self-induced pressure shifts are made using the complex Robert–Bonamy formalism. The results of calculations using different approximations of the intermolecular potential indicate that this is a strong collision system. The effects of the imaginary components on the half-widths are studied. The temperature, vibrational, and rotational state dependence of the half-width are investigated. Results are compared with measurements from the database of self-broadening of water vapor [Gamache RR, Hartmann J-M. An intercomparison of measured pressure-broadening and pressure-shifting parameters of water vapor. Can J Chem 2004; 82: 1013–27].

Measurements of positions, strengths and self-broadened widths of H 2O from 2900 to 8000 cm −1: line strength analysis of the 2nd triad bands

High-resolution spectra of H 2O were recorded with a Fourier-transform spectrometer covering H 2O transitions from 2900 to 8000 cm −1. Over 13,000 absorptions were measured to determine line positions, strengths and self-broadened half-width coefficients. The H 2 16O line strengths of the (0 3 0)–(0 1 0), (1 1 0)–(0 1 0), (0 1 1)–(0 1 0) and (0 3 0)–(0 0 0), (1 1 0)–(0 0 0), (0 1 1)–(0 0 0) bands were fitted to a quantum mechanical model which involves the interactions between the (0 3 0), (1 1 0), and (0 1 1) vibrational states. Also fitted were experimental strengths of the hot bands; (1 2 0)–(0 1 0) and (0 2 1)–(0 1 0). The model includes 14 dipole matrix elements for B- and A-type transitions. The measured line positions were used along with hot water emission measurements (for the (0 3 0), (0 4 0), and (0 5 0) states of H 2 16O) in an analysis to obtain high-accuracy energy level values in the (0 3 0), (1 1 0), (0 1 1), (0 4 0), (1 2 0), (0 2 1), (2 0 0), (1 0 1), (0 0 2), and (0 5 0) vibrational states of H 2 16O and the (1 1 0) and (0 1 1) states of H 2 17O. Also included were measurements and analysis of self-broadened half-widths for over 4700 absorptions between 4405 and 7729 cm −1. The results from this investigation provide new information for the noted H 2 17O bands and present a more accurate representation of the measured H 2 16O bands.

Measurement of ultraweak transitions in the visible region of molecular oxygen

A highly sensitive cavity-enhanced frequency modulation spectroscopy technique has been used to measure ultraweak transitions in molecular oxygen that had not previously been characterized. The self-broadened half-width and line intensity of the measured transitions are reported. We include 12 high J transitions in the b 1 Σ g + ( v ′ = 0 ) ← X 3 Σ g - ( v ″ = 0 ) band of 16O 2 (the so-called A band), 59 transitions in the b 1 Σ g + ( v ′ = 1 ) ← X 3 Σ g - ( v ″ = 1 ) hot band of 16O 2, and 17 high J transitions in the b 1 Σ g + ( v ′ = 0 ) ← X 3 Σ g - ( v ″ = 0 ) band of 16O 18O. Our measurements of line positions of the 16O 18O transitions are used to determine improved molecular constants for the b 1 Σ g + ( v ′ = 0 ) excited state of 16O 18O.

CDSD-1000, the high-temperature carbon dioxide spectroscopic databank

We present a high-temperature version, CDSD-1000, of the carbon dioxide spectroscopic databank. The databank contains the line parameters (positions, intensities, air- and self-broadened half-widths and coefficients of temperature dependence of air-broadened half-widths) of the four most abundant isotopic species of the carbon dioxide molecule. The reference temperature is T ref =1000 K and the intensity cutoff is I cut =10 −27 cm −1/ molecule cm −2 . More than 3 million lines covering the 260–8310, 418–2454, 394–4662, and 429– 2846 cm −1 spectral ranges for 12 C 16 O 2 , 13 C 16 O 2 , 12 C 16 O 18 O , and 12 C 16 O 17 O , respectively, are included in CDSD-1000. The databank has been generated within the framework of the method of effective operators and based on the global fittings of spectroscopic parameters (parameters of the effective Hamiltonians and effective dipole moment operators) to observed data collected from the literature. Line-by-line simulations of several low- and medium-resolution high-temperature ( T=800– 3000 K ) spectra have been performed in order to validate the databank. Comparisons of CDSD-1000 with other high-temperature databanks HITEMP, HITELOR, and EM2C are also given. CDSD-1000 is able to reproduce observed spectra in a more satisfactory way than the high-resolution databank HITEMP for temperatures higher than 1000 K . The databank is useful for studying high-temperature radiative properties of CO 2. CDSD-1000 is freely accessible via the Internet.

Intensities, collision-broadened half-widths, and collision-induced line shifts in the second overtone band of [formula omitted

Absolute intensities, self-broadened half-widths, air-broadened half-widths, self-induced and air-induced line shifts were measured in the second overtone (3-0) band of 12 C 16 O at 298 K using a Fourier-transform spectrometer and a multi-spectral-line-fitting technique. The absolute intensity of the band was determined to be (4.62±0.06)×10 −22 cm molecule −1 . The square of the transition moment, | μ 0| 2, of this band was deduced to be (1.712±0.004)×10 −7 Debye 2 . Herman–Wallis factors were estimated to be C=(1.185±0.009)×10 −2 and D=(1.014±0.069)×10 4. While the line widths were nearly the same as those in the 1-0 and 2-0 bands in both of the cases of broadening studied, the collision-induced line shifts were found to be much larger in the 3-0 band.