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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.

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 ν 2 + ν 3 band of 12 CH 4 . 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 ν 2 + ν 3 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.

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.

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.

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 16 O 12 C 16 O 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 16 O 13 C 16 O as well as the weak hot bands 31112 ← 01101, 32212 ← 02201, 40012 ← 10001, and 40013 ← 10002 of 16 O 12 C 16 O 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 CO 2 . This is also the first study where line mixing parameters have been experimentally determined for any parallel CO 2 band.

The temperature-dependences of line broadening and shift parameters for many 12CH3D transitions have been determined using six high-resolution, high signal-to-noise ratio, room-temperature CH3D (98% purity) and CH3D-N2 spectra recorded with 25 cm path length ( at 0.01 cm−1 unapodized resolution) using the McMath−Pierce FTS located on Kitt Peak, Arizona, and 17 additional high quality, pure CH3D (99% purity) and CH3D-N2 spectra recorded between 79 and 296 K with the 20.38 cm path coolable cell (at 0.0056 cm−1 unapodized resolution) with the Bruker 125HR FTS at the Jet Propulsion Laboratory (JPL), Pasadena, California. The spectra have been fitted simultaneously applying a multispectrum nonlinear least-squares technique. In the analysis, the Lorentzian N2-broadened half-width coefficients and the corresponding pressure-shift coefficients as well as their temperature dependences are extracted for about 400 transitions (0≤J″≤19, K″≤16) in the perpendicular (ΔK=±1) ν6 band. At 296 K, the measured N2-broadened half-width coefficients range from 0.0209 to 0.0782 cm−1 atm−1 whereas the majority of the associated N2-induced shift coefficients are negative, and the values are between -0.016 and 0.005 cm−1 atm−1. The temperature dependence exponents for N2-broadened half-widths range between 0.264 and 0.924, whereas the temperature dependence coefficients for N2-induced shifts are between 0 and 0.00011 cm−1 atm−1 K−1. The N2-broadened half-width coefficients have been also calculated using a semi-classical approach based on a rigorous treatment of the active molecule as a symmetric top, a model intermolecular potential comprising both short- and long-range interactions, and exact classical trajectories. The role of the various high-order multipoles in the line-broadening at low, middle and high values of the rotational quantum number J″ has been investigated and the main features of the K-dependences analyzed. The calculations performed for 296, 240 and 190 K have allowed to deduce the half-width temperature-dependence exponents, completing the general comparison of our new experimental results with those which are available in the literature.

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: b 0 = exp ∑ i a ( i ) x ( i ) for widths where x ( 1 ) = 1 , x ( 2 ) = m , x ( 3 ) = m 2 , x ( 4 ) = m 3 , x ( 5 ) = m 4 , x ( 6 ) = 1 m , and d 0 = ∑ i a ( i ) x ( i ) for pressure shifts where x ( 1 ) = 1 , x ( 2 ) = 1 m , x ( 3 ) = m , x ( 4 ) = m 2 , x ( 5 ) = 1 m 2 , x ( 6 ) = 1 m 3 , x ( 7 ) = m 3 , x ( 8 ) = m m The modeled width coefficients generally agree with the experimental values with standard deviations of less than 1%, while the standard deviations of the modeled values for the pressure-induced shift coefficients range between 2.3% and 6.7%. The largest percentage error is associated with the system of the three hot bands: 21111 ← 01101, 21112 ← 01101, and 21113 ← 01101. It is observed that transitions with the same rotational quantum numbers have slightly different widths in some of the bands. As expected, pressure-induced-shift coefficients vary as a function of the band center, but there are also subtle differences from band to band for transitions with the same rotational quanta.

Line positions and strengths of 12 C 16 O 2 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 CO 2 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.

The temperature dependence of air-broadened halfwidths are reported for some 500 transitions in the (000)-(000) and (010)-(000) bands of H2(16)O using gas sample temperatures ranging from 241 to 388 K. These observations were obtained from infrared laboratory spectra recorded at 0.006 to 0.011 cm(exp-1) resolution with the McMath-Pierce Fourier transform spectrometer located at Kitt Peak. The experimental values of the temperature dependence exponents, eta, were grouped into eight subsets and fitted to empirical functions in a semi-global procedure. Overall, the values of eta were found to decrease with increasing rotational quantum number J. The number of measurements (over 2200) and transitions (586) involved exceeds by a large margin that of any other comparable reported study.

We report measured Lorentz O2-broadening and O2-induced pressure-shift coefficients of CH3D in the nu(exp 2) fundamental band. Using a multispectrum fitting technique we have analyzed 11 laboratory absorption spectra recorded at 0.011 cm(exp 1) resolution using the McMath-Pierce Fourier transform spectrometer, Kitt Peak, Arizona. Two absorption cells with path lengths of 10.2 and 25 cm were used to record the spectra. The total sample pressures ranged from 0.98 to 339.85 Torr with CH3D volume mixing ratios of 0.012 in oxygen. We report measurements for O2 pressure-broadening coefficients of 320 nu(exp 2) transitions with quantum numbers as high as J0(sup w) = 17 and K = 14, where K(sup w) = K' is equivalent to K (for a parallel band). The measured O2-broadening coefficients range from 0.0153 to 0.0645 cm(exp -1) atm(exp -1) at 296 K. All the measured pressure-shifts are negative. The reported O2-induced pressure-shift coefficients vary from about -0.0017 to -0.0068 cm(exp -1) atm(exp -1). We have examined the dependence of the measured broadening and shift parameters on the J(sup W), and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = -J(sup W), J(sup W), and J(sup w) + 1 in the QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.4%. The O2-broadening and pressure shift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom-atom Lennard-Jones potential. The theoretical results of the broadening coefficients are generally larger than the experimental data. Using for the trajectory model an isotropic Lennard-Jones potential derived from molecular parameters instead of the spherical average of the atom-atom model, a better agreement is obtained with these data, especially for |m

In this paper, we report measured Lorentz self-broadening and self-induced pressure-shift coefficients of 12CH3D in the ν2 fundamental band (ν0 ≈ 2200 cm−1). The multispectrum fitting technique allowed us to analyze simultaneously seven self-broadened absorption spectra. All spectra were recorded at the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory (NSO) on Kitt Peak, AZ with an unapodized resolution of 0.0056 cm−1. Low-pressure (0.98–2.95 Torr) as well as high-pressure (17.5–303 Torr) spectra of 12C-enriched CH3D were recorded at room temperature to determine the pressure-broadening coefficients of 408 ν2 transitions with quantum numbers as high as J″ = 21 and K = 18, where K″ = K′ ≡ K (for a parallel band). The measured self-broadening coefficients range from 0.0349 to 0.0896 cm−1 atm−1 at 296 K. All the measured pressure-shifts are negative. The reported pressure-induced self-shift coefficients vary from about −0.004 to −0.008 cm−1 atm−1. 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 QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 3.6%. A semiclassical theory based upon the Robert–Bonamy formalism of interacting linear molecules has been used to calculate these self-broadening and self-induced pressure-shift coefficients. In addition to the electrostatic interactions involving the octopole and hexadecapole moments of CH3D, the intermolecular potential includes also an atom–atom Lennard–Jones model. For low K (K ⩽ 3) with |m| ⩽ 8 the theoretical results of the broadening coefficients are in overall good agreement (3.0%) with the experimental data. For transitions with K approaching |m|, they are generally significantly underestimated (8.8%). The theoretical self-induced pressure shifts, whose vibrational contribution is derived from results in the QQ-branch, are generally smaller in magnitude than the experimental data in the QP-, and QR-branches (15.2%).

The space-based Orbiting Carbon Observatory (OCO) mission will achieve global measurements needed to distinguish spatial and temporal gradients in the CO2 column. Scheduled by NASA to launch in 2008, the instrument will obtain averaged dry air mole fraction ( X CO 2 ) with a precision of 1 part per million (0.3%) in order to quantify the variation of CO2 sources and sinks and to improve future climate forecasts. Retrievals of X CO 2 from ground-based measurements require even higher precisions to validate the satellite data and link them accurately and without bias to the World Meteorological Organization (WMO) standard for atmospheric CO2 observations. These retrievals will require CO2 spectroscopic parameters with unprecedented accuracy. Here we present the experimental and data analysis methods implemented in laboratory studies in order to achieve this challenging goal. To cite this article: C.E. Miller et al., C. R. Physique 6 (2005).

Room temperature Lorentz air-broadened halfwidth and pressure-induced air-shift coefficients were measured for 1011 transitions in the octad region of methane between 4100 and 4635 cm −1 . These measurements were made by analyzing 10 laboratory absorption spectra recorded at 0.011 cm −1 resolution using the McMath–Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 2.05 and 150 cm. The total sample pressures ranged from 99 to 400 torr with CH 4 volume mixing ratios of 0.01 in dry air. The spectral line parameters were retrieved using a multispectrum nonlinear least squares technique. Transitions belonging to five bands of the octad polyad were observed, namely ν 2 + 2 ν 4 , ν 1 + ν 4 , ν 3 + ν 4 , 2 ν 2 + ν 4 , and ν 2 + ν 3 . The numbers of measurements by bands are: 33 for ν 2 + 2 ν 4 , 180 for ν 1 + ν 4 , 635 for ν 3 + ν 4 , 33 for 2 ν 2 + ν 4 , and 130 for ν 2 + ν 3 . Transitions with rotational quantum number J up to 16 are included in the analysis. The measured width and shift coefficients vary according to the tetrahedral symmetry species and the rotational quantum numbers of the transitions. The retrieved parameters from this study are compared with prior results, in part to estimate absolute accuracy and determine the extent of vibrational dependence of widths and shifts.

A semiclassical theory based upon the Robert–Bonamy formalism has been developed to explain the experimental measurements of self-broadening, self-induced pressure shift coefficients in the ν1,ν2, 2ν2 bands of H12C14N and the 2ν1 band of H13C14N, as well as the temperature dependences of these parameters with special emphasis on the ν2 band. Our calculations include only electrostatic interactions and neglect the vibrational dependence of the isotropic part of the intermolecular potential, which probably has a weak contribution to the HCN self-shifts for the bands investigated in this study. The agreement between theory and measurements is good in the cases of self-broadening coefficients and their variation with temperature, as well as the self-shift coefficients determined at room temperature. However, the observed temperature dependence of self-shift coefficients in the ν2 band is different from that derived theoretically.

Lorentz pressure-broadening and pressure-induced shift coefficients along with their temperature dependences have been determined for over forty P- and R-branch transitions in the fundamental band of 12 C 16 O broadened with helium. A total of nineteen spectra recorded at various temperatures (+24 to −194 °C) in the 2010–2260 cm −1 spectral region were analyzed simultaneously using a multispectrum nonlinear least squares fitting technique. The spectra were recorded with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak. Present results are compared with similar measurements reported recently.

Line mixing has been measured for two pairs of transitions in the ν 2 band of H 2 16 O. The rotational assignments of the four lines (in terms of the rotational quantum numbers J , K a and K c ) are (a) two P branch lines: (1 0 1)←(2 1 2) mixing with (2 1 2)←(3 0 3) at 1539.061 and 1540.300 cm −1 , respectively; and (b) two R branch lines: (3 0 3)←(2 1 2) mixing with (2 1 2) ←(1 0 1) at 1652.400 and 1653.267 cm −1 , respectively. Pressure broadening coefficients of H 2 O (halfwidths, pressure shifts and off-diagonal relaxation matrix elements) are reported for seven broadeners (self, H 2 , He, CO 2 , N 2 , O 2 and air) from retrievals performed by multispectrum fitting implemented with line mixing. The effect is largest for self- and H 2 -broadening.

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 m2 band of H 12 C 14 N centered near 712 cm � 1 . Infrared spectra of HCN in the 14-lm 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 selfbroadening 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.

Air-broadened linewidths, pressure-induced shift coefficients and their temperature dependences were retrieved for over 1000 transitions in the ν 3 band of 14 N 16 O 2 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.

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 12 C 16 O. 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.

High-resolution (0.005 cm −1 ) infrared absorption spectra of HCN in the 2ν2 band region near 1411 cm −1 have been recorded at room temperature using the Bruker IFS120HR Fourier transform spectrometer located at Pacific Northwest National Laboratory. Four spectra of high-purity (99.8%) HCN together with three spectra of lean mixtures (∼3%) of HCN in dry air were simultaneously fit using a multispectrum nonlinear least-squares procedure. The analysis yielded room temperature values for absolute intensities, self- and air-broadening coefficients, and self- and air-induced pressure shift coefficients for numerous lines in the 2ν20 band of H12C14N. In addition, intensities, self- and air-broadening coefficients for several lines of the 3ν21−ν21 hot band, as well as intensities for a number of lines in the 2ν20 band of H13C14N, were also determined. Since there are no previous measurements of broadening and shift parameters reported in the 2ν20 band, our results are compared with values recently determined in the ν1 band of H12C14N and with current HITRAN values.

Line intensities of the three lowest fundamentals of the 12CH3D Triad are modeled with an RMS of 3.2% using over 2100 observed values retrieved by multispectrum fitting of enriched sample spectra recorded with two Fourier transform spectrometers. The band strengths of the Triad in units of 10−18 cm−1/(molecule cm−2) at 296 K are, respectively, 2.33 for ν6 (E) at 1161 cm−1, 1.75 for ν3 (A1) at 1307 cm−1 and 0.571 for ν5 (E) at 1472 cm−1. The total calculated absorption arising from 12CH3D Triad fundamentals is 4.65×10−18 cm−1/(molecule cm−2) at 296 K. In addition, some 740 intensities of nine hotbands are fitted to 8.1%; most of the hotband measurements belong to 2ν6−ν6 and ν3+ν6−ν3 near 1160 cm−1, 2ν3−ν3 near 1290 cm−1 and ν3+ν6−ν6 near 1304 cm−1. The other observed hotbands are ν5+ν6−ν6, 2ν5−ν5, ν5+ν6−ν5, ν3+ν5−ν3, and ν3+ν5−ν5.

We have analyzed the methyl fluoride R Q(J,0) Q branch lines located near 1475 cm −1 using a simultaneous multi-spectrum fitting technique. In this analysis we have used previously recorded diode-laser data in which we collected many data points covering only one or two Q branch lines in a particular run. The analysis consists of simultaneously fitting 57 spectra collected with numerous pressure and path length conditions for all absorption lines. The data are concatenated to create one continuous spectrum of the Q branch. We have determined the intensity and self-broadened widths at 296 K for 23 R Q ( J ,0) lines.

Air- and N2-broadening, air- and N2-pressure-induced shift coefficients and the temperature dependence exponent of the broadening coefficients and the temperature dependent coefficient of pressure-induced shifts have been determined for transitions of the ν1 band of H12C14N from 39 laboratory absorption spectra recorded at 0.005 and 0.008 cm −1 resolutions with two different Fourier transform spectrometers. The parameters were retrieved from the multispectrum nonlinear least-squares fits to the 3200– 3400 cm −1 region of spectra recorded at temperatures between +26°C and −60°C. Pure samples of HCN in a 19.95 cell and a 0.958 cm cell at room temperature as well as lean mixtures of HCN in N2 or dry air in a coolable cell with a 50 cm absorption path were used in the experiments. Line parameters for N2 broadening were determined by fitting 27 spectra simultaneously while air-broadening parameters were quantified from simultaneous fits to 22 spectra. The average ratio and the standard deviation of the room-temperature air- to N2-broadening coefficient of lines with assignments between P(29) and R(28) are 0.904±0.001. Pressure-induced shift coefficients at 296 K are all negative with values between 0 and ∼−0.006 cm −1 atm −1 and different rotational dependences in the P- and R-branches. Differences between our results, previous measurements and the parameters that are reported in the 2000 edition of HITRAN (HIgh-resolution TRANsmission) database are quantified and discussed.

Line intensities of the two 12 C 16 O 2 laser bands (ν3–ν1 and ν3–2ν20) centered near 960.9 and 1063.7 cm −1 , respectively, were obtained from analysis of 30 room temperature long path laboratory absorption spectra recorded at 0.0028 and 0.0053 cm −1 resolution with the McMath–Pierce Fourier transform spectrometer at the National Solar Observatory (located on Kitt Peak). The spectra were analyzed simultaneously with the multispectrum nonlinear least-squares fitting procedure. The measured line intensities were further analyzed to derive the vibrational band intensities and Herman–Wallis coefficients.

In this study we report the first high-resolution measurements of pressure broadening and pressure-induced shift coefficients due to nitrogen for rovibrational transitions in the ν3 band of 13 C 16 O 2 . N2 broadening and shift coefficients of ν 3 12 C 16 O 2 transitions were also measured. In addition, nitrogen-broadening coefficients for many transitions in the ν3+ν2−ν2 hot band of 13 C 16 O 2 as well as the ν3 band of 13 C 16 O 18 O were also determined. The results were obtained by analyzing five high-resolution ( 0.0028 cm −1 ) room temperature laboratory absorption spectra with a multispectrum nonlinear least-squares spectral fitting technique. The data were recorded with the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory on Kitt Peak using a 4.08 cm sample cell, total pressures up to 470 Torr , and a 90% 13 C -enriched CO2 sample. For the pressure-broadened spectra the 13 C 16 O 2 volume-mixing ratios were⩽0.5%. Similar to broadening coefficients, the measured pressure shift coefficients were also found to be transition dependent. However, the shift coefficients were different in the P and R branch lines with the same rotational quantum number, J. The measured nitrogen-broadening coefficients range from 0.0960 to 0.0643 cm −1 atm −1 at 296 K . The measured shift coefficients were all negative and varied between 0 and −0.0036 cm −1 atm −1 . The results obtained are compared with other values reported in the literature.

Extensive high-resolution experimental determination is provided for air- and N2-broadening and pressure shift coefficients for the two 13 C 16 O 2 laser bands (located at 913.4 and 1017.6 cm −1 , respectively), in addition to new measurements of self-broadening and self-shift coefficients for the 12 C 16 O 2 laser bands. These parameters were determined from analysis of spectra recorded with the McMath–Pierce Fourier transform spectrometer (FTS) of the National Solar Observatory on Kitt Peak, Arizona. We used a multispectrum nonlinear least-squares fitting technique to analyze 30 long path, room temperature absorption spectra. By combining the spectra of 12 CO 2 and 13 CO 2 in the same fit we were able to obtain a consistent set of line parameters for both molecules. The results obtained for the 12 CO 2 and 13 CO 2 laser bands were compared with each other, with values in the HITRAN database, and with values reported in the literature for CO2 bands. Comparisons revealed no significant differences in the broadening or shift coefficients between the two laser bands. The coefficients determined for the two isotopomers agreed closely.

Self- and hydrogen-broadening coefficients and pressure-shift coefficients for the first overtone band transitions of 12 C 16 O at room temperature have been determined through analysis of nine high-resolution (0.0055 cm −1 ) absorption spectra. These spectra were recorded using the 1-m Fourier transform spectrometer (FTS) at the McMath-Pierce facility of the National Solar Observatory on Kitt Peak, Arizona. Because of the short path length of the sample cell (10.0 cm ) , the volume mixing ratios of CO in hydrogen were relatively high, ∼18–22%, to achieve measurable absorption. These large volume-mixing ratios necessitated the simultaneous determination of the CO self-broadening and self-shift coefficients along with the hydrogen-broadening and hydrogen-induced shift coefficients. We have determined these coefficients at room temperature, along with line positions and absolute intensities, for the P(27) through R(27) 12 C 16 O 2-0 transitions by fitting the entire spectral interval from 4130 to 4345 cm −1 in all nine spectra simultaneously using our multispectrum nonlinear least-squares procedure. Our intensity measurements are consistently low (1–6%) compared with the HITRAN values but the majority of the intensities are within 4% of the HITRAN values. The values of self-broadening coefficients vary from 0.0452 to 0.0862 cm −1 atm −1 at 296 K and those of hydrogen-broadening coefficient range between 0.0475 and 0.0795 cm −1 atm −1 at 296 K . All of our measured self- and hydrogen-shift coefficients are negative and range from −0.002 to −0.008 cm −1 atm −1 . With the pressure and path length used in our study we did not find evidence of significant line mixing in either the self- or hydrogen-broadened spectra. This study represents the first high-resolution experimental determination of hydrogen-induced pressure broadening and pressure-shift coefficients in the 2-0 band of 12 C 16 O at room temperature.

We report the first measured Lorentz self- and nitrogen-broadening and the corresponding pressure-shift coefficients in the ν5(E) perpendicular band of 12CH3D between 1275 and 1600 cm −1 . The multispectrum fitting technique allowed us to analyze simultaneously both self-broadened and N2-broadened spectra recorded at 0.005 to 0.006-cm−1 resolution with a Fourier transform spectrometer located at Kitt Peak. Self-broadening coefficients for over 550 transitions and self-shift coefficients for more than 480 transitions with rotational quantum numbers up to J″=17 and K″=14 were determined. Nitrogen-broadening and nitrogen pressure-induced shift coefficients were determined for more than 300 of those transitions. The measured broadening coefficients vary from 0.020 to about 0.091 cm −1 atm −1 at 296 K . The measured pressure-shift coefficients had values extending from about −0.014 to +0.005 cm −1 atm −1 . Very few of the pressure-shift coefficients were positive, and the positive pressure-shift coefficients were mostly associated with the J″=K″ transitions in the PQ sub-bands. The J″=K″ transitions in the PP and RR sub-bands were associated with the smallest broadening coefficients. Our measurements also included 46 forbidden lines with Δ K=±2 (10 O P , 9 O Q ,3 Q P , 7 Q Q , 1 Q R , 13 S Q and 3 SR). The off-diagonal relaxation matrix element coefficients, Wij, in cm −1 atm −1 at 296 K which are associated with line mixing were determined for a few transitions with K″=3 (A+A−splitting) in the P P , P Q and RP sub-bands. We have examined the dependence of the measured parameters on J,K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of J and K.

Isotopic ozone lines of 16O16O17O and 16O17O16O in the 5 μm region are identified for the first time in balloon-borne high-resolution (0.003 cm −1 ) solar absorption spectra. A few of these lines also are observed in ground-based spectra. These lines need to be included in analysis of atmospheric absorption spectra, in addition to the recently identified 16 O 16 O 18 O , 16 O 18 O 16 O and 16O12C34S lines in this region.

Lorentz self- and nitrogen-broadening coefficients as well as self- and nitrogen-pressure induced shift coefficients were measured at room temperature for more than 440 transitions in the QP, QQ and QR branches of the ν3(A1) parallel band of 12CH3D. The simultaneous multispectrum nonlinear least-squares fitting analysis was performed in the 1140– 1440 cm −1 region using 14 spectra of room temperature gas recorded with the McMath–Pierce Fourier transform spectrometer ( 0.005 cm −1 unapodized resolution) of the National Solar Observatory (NSO) on Kitt Peak. The measured self-broadening coefficients varied from about 0.025 cm −1 atm −1 at 296 K for high J, K transitions to about 0.09 cm −1 atm −1 at 296 K for low J, K transitions. In the case of nitrogen broadening these values ranged from about 0.023 to 0.073 cm −1 atm −1 at 296 K . The majority (>90%) of the self-pressure induced shift coefficients as well as nitrogen-pressure-induced shift coefficients was negative with values varying between approximately 0 and −0.012 cm −1 atm −1 . However, similar to air-induced pressure-shift coefficients determined in an earlier study, the measured self- and nitrogen-induced pressure-shift coefficients were positive for the QR-branch transitions with J″=K″, varying from 0 to about +0.009 cm −1 atm −1 . Weak line mixing effects were observed in several high-J lines with K″=3 splitting and approximate values for the off-diagonal relaxation matrix-element coefficients were determined for a few A 1 A 2 (A + A − ) split components. Comparisons are made between the measured self- and nitrogen-broadening and shift coefficients, and the results are also compared with measurements in other bands.

A multispectrum nonlinear least-squares fitting technique has been applied to determine accurate zero-pressure line center positions, Lorentz self- and N2-broadening coefficients and self- and N2-induced pressure shift coefficients of transitions in the ν6 (E) perpendicular band of 12CH3D between 1035 and 1270 cm −1 . Seventeen high-resolution (0.002– 0.006 cm −1 ) room temperature absorption spectra recorded with two Fourier transform spectrometers (FTS) were analyzed together. Self-broadening coefficients for over 700 transitions and self-shift coefficients for more than 600 transitions were determined. Measurements of nitrogen-broadening coefficients for more than 480 transitions and nitrogen pressure induced shift coefficients for nearly 430 transitions were also made. The measurements include transitions with rotational quantum numbers as high as J″=18 and K″=15 and several forbidden transitions. The measurements were made in all six sub-bands ( P P , P Q , P R , R P , R Q and RR). The measured self-broadening coefficients vary from 0.025– 0.096 cm −1 atm −1 at 296 K and the N2-broadening coefficients from 0.02 to 0.08 cm −1 atm −1 at 296 K . Self-induced-shift coefficients range from −0.014 to +0.004 cm −1 atm −1 while the nitrogen-induced-shift coefficients vary from −0.013 to +0.008 cm −1 atm −1 . Very few of the measured pressure-shift coefficients were positive, and the positive shift coefficients were mostly associated with the J″=K″ transitions in the PQ sub-bands. The off-diagonal relaxation matrix element coefficients of a number of transitions with K″=3 doublets for both self- and N2-broadening were also obtained. The results obtained with the two different broadening gases are compared and discussed. Comparisons with previous values from the literature are also made.

High-resolution, high signal-to-noise spectra of a high-purity (99%) mono-substituted 13C-enriched ethane (13C12CH6) in the ν12 fundamental band near 12.2 μm region were recorded with a Bruker IFS 125HR Fourier transform spectrometer. The data were obtained for four sample pressures at three different temperatures (130–208 K) using a 20.38-cm long coolable absorption cell. The spectra were fitted simultaneously to retrieve individual line positions and absolute line intensities for 1660 absorption features. A multispectrum nonlinear least squares spectrum fitting technique was employed in the analysis. Constraints were used to fit each pair of doublet components arising from torsional Coriolis interaction of the excited ν12 = 1 state with the nearby excited torsional ν6 = 3 state. Line positions and absolute line intensities were retrieved by simultaneously fitting the four experimental spectra recorded at three low sample temperatures (130 K, 178 K and 208 K). The measured positions and intensities were determined for the standard reference temperature of 296 K and compared with the predicted values listed in the HITRAN database. Calculated line intensities at each of the measured spectrum temperatures are also provided as supplemental data. Integrated intensities are also reported.

JALAL NOROOZ OLIAEE, NASSER MOAZZEN-AHMADI, Department of Physics and Astronomy, University of Calgary, Calgary, AB, Canada; IRVINGOZIER, Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada; KEEYOON SUNG, Jet Propulsion Laboratory, Science Division, California Institute of Technology, Pasadena, CA, USA; TIMOTHY J CRAWFORD, LINDA BROWN, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; EDWARD H WISHNOW, Space Sciences Laboratory and Department of Physics, University of California, Berkeley, CA, USA; V. MALATHY DEVI, Department of Physics, College of William and Mary, Williamsburg, VA, USA.

Absolute intensities of 376 16O3 lines in the 9–11 μm region have been determined from high-resolution infrared absorption spectra recorded at room temperature using a Fourier transform spectrometer. The ozone samples were contained in a glass cell having crossed IR-transmitting and UV-transmitting paths, and the UV absorption at 254 nm was used to monitor ozone concentrations in the cell. A multispectrum nonlinear least squares fitting procedure was used to determine intensities for 366 lines in the ν3 fundamental band and 10 lines in the ν1 band. The absolute accuracy of these intensity values ranges from 2% for the strongest, most well determined lines to 4 or 5% for the weakest lines measured. On average, our measured intensities are approximately 1% larger than the values on current spectroscopic databases.

Air-broadening and shift coefficients for more than 680 transitions in the 1040– 1410 cm −1 spectral region of the ν6 perpendicular band of 12CH3D have been measured. Values have been obtained from analysis of 11 room temperature absorption spectra recorded at 0.005 cm−1 resolution with the McMath–Pierce Fourier transform spectrometer located on Kitt Peak National Solar Observatory and retrieved using a multispectrum nonlinear least-squares fitting technique. The measured broadening coefficients range from 0.016 to 0.077 cm −1 atm −1 at 296 K for transitions up to J″=17 and K″=15, including 34 forbidden lines with 2≤ΔK≤4. The corresponding pressure-induced shift coefficients vary from −0.012 to +0.008 cm −1 atm −1 , and the majority of these are negative. Within each J series in the PP and RR sub-bands, the J″=K″ (and J′=K′) transition exhibited the smallest broadening coefficient. In the PQ sub-band, the J″=K″ transition in each J series of lines had the largest positive pressure-shift coefficient while the largest negative pressure-shift coefficients were associated with the J′=K′ lines in the RQ sub-band. Subsets of the air-broadened width coefficients vary somewhat smoothly as a function of the rotational quanta, and this behavior has been modeled to ±8% using empirical expressions. Finally, Line mixing effects were observed for the first time in several of the K″=3 ( A + A − ) split components in the P P, P Q, P R, R P, R Q and RR sub-band transitions, and values for off-diagonal relaxation matrix coefficients were determined.

A multispectrum nonlinear least-squares fitting technique has been applied to determine Lorentz air-broadening coefficients and air induced pressure-shift coefficients of 12 CH 3 D for the ν 3 fundamental band in the spectral region between 1154 and 1430 cm −1 . This analysis has utilized 11 absorption spectra recorded at an unapodized resolution of 0.005 cm −1 with the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory (NSO) on Kitt Peak. Low pressure spectra (with 1–2.99 Torr of enriched 12 CH 3 D samples) as well as lean mixtures (≈1%) of 12 CH 3 D in dry air (total pressures of 100–400 Torr) at room temperature have been measured to determine the pressure broadening coefficients of more than 360 ν 3 transitions with quantum numbers as high as J ″=17 and K ″=17. The measured air-broadening coefficients range from 0.0155 to 0.0726 cm −1 atm −1 at 296 K. The pressure-induced shift coefficients vary from about −0.0086 to +0.0058 cm −1 atm −1 . The majority of the shifts are negative, and the positive shifts often involve transitions with J ″= K ″. Weak line mixing effects have also been observed in a few high J lines with K ″=3 and approximate off diagonal relaxation matrix coefficients were determined for several A + A − (A1A2) split components. At low to medium values of J , the A + A − splitting is extremely small, and the two components are practically unresolved. Variations of the measured parameters with the A- and E- symmetry species and the rotational quantum numbers of the transitions involved are discussed. The present results are compared to the few available experimental values in the literature.

We describe the updates to the spectroscopic parameters of ozone and its isotopes in the 1996 HITRAN compilation. Recent published studies not included in HITRAN are also summarized. Finally, we report the identification of infrared lines of the v(sub 3) bands of O-16O-16O-17 and O-16O-17O-16 in high-resolution solar spectra recorded by stratospheric balloon-borne and ground-based Fourier transform spectrometers.

A multispectrum nonlinear least-squares fitting technique has been used to determine the absolute intensities for approximately 1500 spectral lines in 36 vibration - rotation bands Of C-12O2-16 between 3090 and 3850/ cm. A total of six absorption spectra of a high- purity (99.995% minimum) natural sample of carbon dioxide were used in the analysis. The spectral data (0.01/cm resolution) were recorded at room temperature and low pressure (1 to 10 Torr) using the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory (NSO) on Kitt Peak. The absorption path lengths for these spectra varied between 24.86 and 385.76 m. The first experimental determination of the intensity of the theoretically predicted 2(nu)(sub 2, sup 2) + nu(sub 3) "forbidden" band has been made. The measured line intensities obtained for each band have been analyzed to determine the vibrational band intensity, S(sub nu), in /cm/( molecule/sq cm) at 296 K, square of the rotationless transition dipole moment |R|(exp 2) in Debye, as well as the nonrigid rotor coefficients. The results are compared to the values listed in the 1996 HITRAN database which are obtained using the direct numerical diagonalization (DND) technique as well as to other published values where available.

High quality and precise measurements of self-broadened and self-shift coefficients in the fundamental band of 12C16O were made using spectra recorded at room temperature with the high-resolution (0.0027 cm-1) McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectral region under investigation (2008–2247 cm-1) contains the P(31) to R(31) transitions. The data were obtained using a high-purity natural isotopic sample of carbon monoxide and two absorption cells with pathlengths of 4.08 and 9.98 cm, respectively. Various pressures of CO were used, ranging between 0.25 and 201.2 Torr. The results were obtained by analyzing five spectra simultaneously using a multispectrum nonlinear least-squares fitting technique. The self-broadened coefficients ranged from 0.0426(2) cm-1 atm-1 at 296 K to 0.0924(2) cm-1 atm-1 at 296 K, while the pressure-induced shift coefficients varied between −0.0042(3) cm-1 atm-1 at 296 K and +0.0005(1) cm-1 atm-1 at 296 K. The value in parentheses is the estimated uncertainty in units of the last digit. The self-broadened coefficients of lines with same values of m in the P and R branches agree close to within experimental uncertainties while the self-shift coefficients showed considerable variation within and between the two branches. The mean value of the ratios of P branch to R branch self-broadened coefficients was found to be 1.01 with a standard deviation of ±0.01. Comparisons of the results with other published data were made.

In this study we report the first measurements of the pressure broadening and the pressure-induced line shift coefficients due to air and nitrogen for 93 individual rovibrational lines, P(46) to R(46) and P(50) to R(45), respectively, belonging to the 2ν02 and ν1 bands of 16O13C18O. The results were obtained by analyzing ten long path, high-resolution laboratory absorption spectra using a multispectrum nonlinear least-squares technique. Broadening due to nitrogen was about 4% larger than by air. Similar to broadening coefficients, the pressure-shift coefficients were found to be transition dependent, but different for the P- and R-branch lines with the same rotational quantum number, J. Except for a few R-branch lines, the measured shift coefficients were negative. The shift coefficients varied from +4×10-3 cm-1 atm-1 at 296 K to −5.6×10-3 cm-1 atm-1 at 296 K. Comparisons of the broadening and shift coefficients between the two bands, between the P and R branches, and between the two broadening gases are reported. No significant difference between shift coefficients of the two bands or the two broadening gases was observed. The results obtained were compared with those reported in the literature for the more abundant 12C16O2 species.

In this paper we report the pressure broadening and the pressure-induced line shift coefficients for 46 individual rovibrational lines in both the (12)C(16)O2, 00(sup 0)1-(10(sup 0)0-02(sup 0)0)I, and 00(sup 0)1-(10(sup 0)0-02(sup 0)0)II, laser bands (laser band I centered at 960.959/cm and laser band II centered at 1063.735/cm) determined from spectra recorded with the McMath-Pierce Fourier transform spectrometer. The results were obtained from analysis of 10 long-path laboratory absorption spectra recorded at room temperature using a multispectrum nonlinear least-squares technique. Pressure effects caused by both air and nitrogen have been investigated. The air-broadening coefficients determined in this study agree well with the values in the 1996 HITRAN database; ratios and standard deviations of the ratios of the present air-broadening measurements to the 1996 HITRAN values for the two laser bands are: 1.005(15) for laser band I and 1.005(14) for laser band II. Broadening by nitrogen is 3 to 4% larger than that of air. The pressure-induced line shift coefficients are found to be transition dependent and different for the P- and R-branch lines with same J" value. No noticeable differences in the shift coefficients caused by air and nitrogen were found. The results obtained are compared with available values previously reported in the literature.

High-resolution FTIR data of carbonyl fluoride in the region of the C-O stretch nu1 fundamental have been analyzed. Satisfactory interpretation of the spectral data required a rigorous analysis that involved the inclusion of Fermi resonance with the 2nu2 state and Coriolis interaction with the 2nu3 + nu6 dark state. Deperturbed molecular constants for the three interacting states as well as perturbation parameters that fit the data within the limits of the experimental accuracy of approximately 0.00035 cm-1 have been obtained. Interesting evidence of "axis interchange" in the 2nu2 state has been observed. Copyright 1997 Academic Press. Copyright 1997Academic Press

Room temperature measurements of self- and air-broadening coefficients are reported for over 370 transitions covering a range of 0/= J"/= 45 and 1/= Ka"/= 12 for the nu2 ozone band in the 630 to 800 cm-1 spectral region. In addition, the temperature dependence of air-broadened halfwidth and air-induced pressure shift coefficients have been determined for over 350 spectral lines. A total of 29 O3 absorption spectra (0.005-cm-1 resolution) recorded at various temperatures (29 to -63deg;C) with a Fourier transform spectrometer were used in the analysis. The spectral line parameters were deduced by analyzing all of the 29 spectra simultaneously using a nonlinear least-squares fitting technique. The results are compared with similar measurements obtained in the ozone nu1 band. Copyright 1997Academic Press

An extension of the nonlinear least squares spectrum fitting technique has been developed for the simultaneous fitting of multiple spectra. This procedure's smaller number of fitted parameters as compared to fitting one spectrum at a time improves the determination of spectroscopic parameters. A more reliable evaluation of the errors associated with the solution is possible. Correlations among fitted parameters may preclude their determination from a single spectrum fit. If the correlations differ from spectrum to spectrum, however, separation of these parameters is often possible when including the spectra in one solution. Overfilling is also avoided when combining spectra with sufficiently different experimental physical conditions.

We describe atmospheric validation of View the MathML source and View the MathML source CO_2 absorption coefficient databases for use by the Orbiting Carbon Observatory (OCO-2). The OCO-2 mission will collect the measurements needed to estimate column-averaged CO_2 dry air mole fraction within 1 ppm accuracy without the region- or airmass-dependent biases that would significantly degrade efforts to understand carbon sources and sinks on a global scale. To accomplish this, the forward radiative transfer model used to generate synthetic atmospheric spectra for retrievals must achieve unprecedented spectroscopic fidelity within the short wave infrared CO_2 bands sampled by the sensors. The failure of Voigt line shapes and conventional line mixing formulations for such objectives has motivated significant revisions to line shape models used to generate the gas absorption cross sections for the OCO-2 forward model. In this paper, we test line mixing and speed dependent line shapes combined with improved experimental line parameters. We evaluate pre-computed absorption coefficients in the two spectral regions of CO_2 absorbtion using high resolution FT-IR laboratory spectra, atmospheric spectra from the Total Carbon Column Observing Network (TCCON), and medium resolution soundings from the space-based Greenhouse Gases Observing Satellite (GOSAT).

High-resolution (0.01/cm) absorption spectra of lean mixtures of CH4 in dry air were recorded with the McMath-Pierce Fourier transform spectrometer (FTS) of the National Solar Observatory on Kitt Peak at various temperatures between 24 and -61 C. The spectra have been analyzed to determine the values at room temperature of pressure-broadened widths and pressure-induced shifts of more than 740 transitions. The temperature dependence of air-broadened widths and pressure-induced shifts was deduced for approx. 370 transitions in the nu(sub 1) + nu(sub 4), nu(sub 3) + nu(sub 4), and nu(sub 2) + nu(sub 3) bands of (12)CH4 located between 4118 and 4615/cm. These results were obtained by analyzing a total of 29 spectra simultaneously using a multi-spectral non-linear least-squares fitting technique. This new technique allowed the determination of correlated spectral line parameters (e.g. intensity and broadening coefficient) better than the procedure of averaging values obtained by fitting the spectra individually. This method also provided a direct determination of the uncertainties in the retrieved parameters due to random errors. For each band analysed in this study the dependence of the various spectral line parameters upon the tetrahedral symmetry species and the rotational quantum numbers of the transitions is also presented.

Results are presented of an analysis of 29 room-temperature laboratory absorption spectra of a dilute CH4 sample in dry air, N2, and O2 at total pressures ranging from 60 to 550 torr, yielding values of pressure-broadening and pressure-induced-shift coefficients for more than 450 vibration-rotation transitions in the nu(3), nu(2) + nu(4), and 2nu(2)-super-2 bands of (C-12)H4. Comparisons of the present results for the nu(3) and nu(2) + nu(4) bands with previous measurements on other bands and isotopes of CH4 show that, for a given transition, broadening by air and N2 are nearly equal, and broadening by O2 is smaller by less than 10 percent. It is also found that the pressure shift coefficients are more vibrational dependent than the pressure broadening coefficients.