A variety of phenomenological line-shape models are compared with a speed-dependent Blackmore profile describing an O-2 spectral line. Multispectrum fitting techniques and quality of the fit parameter were used to quantify this comparison. It allowed to indicate which models are adequate for analysis of spectra measured with a given signal to noise ratio. This research has an impact on interpretation of spectral analysis results, improvement of spectroscopic databases, atmospheric remote sensing, trace gas metrology, and Doppler thermometry.

Precise N2, O2, H2, Ar, He, and self-broadenings and shifts have been obtained for Q- and R-branch transitions in the ν1 fundamental band of ammonia from simultaneous fits of low-noise, high-resolution difference-frequency laser spectra at pressures from 0.07 to 27kPa (0.5–200Torr). Observed lineshapes exhibit significant deviations from the conventional Voigt profile, which may be attributed to Dicke narrowing and/or speed-dependent broadening. At the higher pressures, line mixing is evident and must be included in the fits. For self-broadening, line mixing is dominated by collisional tunneling transitions, whereas for the non-polar buffers, rotational relaxation among selected K states is the primary mixing mechanism.

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 80kPa (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.

Two editions of the methane line parameters (line positions, intensities and broadening coefficients) available from HITRAN in 2000 and 2001 are described. In both versions, the spectral interval covered was the same (from 0.01 to 6184.5cm−1), but the database increased from 48,033 transitions in 2000 to 211,465 lines in 2001 because weaker transitions of 12CH4 and new bands of 13CH4 and CH3D were included. The newer list became available in 2001 in the “Update” section of HITRAN. The sources of information are described, and the prospects for future improvements are discussed.

First-order line-mixing coefficients and model relaxation matrix element scaling factors have been obtained for allowed transitions in the ν3 band Q branch of CH4 broadened by H2, He, N2, O2, Ar, and CH4. The broadening, shifting, Dicke-narrowing, and line-mixing parameters are determined by simultaneous least-squares fitting of spectra at pressures from 0.014 to 66.66 kPa recorded with a high-resolution difference-frequency laser. These results confirm, improve, and extend a previous analysis of the lower pressure (⩽13.3 kPa) data [A.S. Pine, J. Chem. Phys. 97 (1992) 773] which yielded averaged coefficients of individually fit spectra where adjacent broadened lines are still partially resolved.

Starting with the transport/relaxation equation in the impact limit we have developed some new analytical and numerical approaches for modelling pressure-broadened spectral profiles of isolated atomic or molecular lines. Particular attention is paid to the influence of velocity-changing collisions on the line shape described by the speed-dependent broadening and shifting rates. These new models are compared to existing high-resolution experimental spectra.

We have generalized the combined strong and weak Dicke-narrowed spectral profile of Rautian and Sobel'man (Sov Phys Usp 1967;9:701–16) for speed-dependent broadening and shifts partially correlated with hard and/or soft velocity-changing collisions. The proposed line shape model is tested on Ar-broadened HF spectra.

We analyze the high-resolution asymmetric spectral lines of Ar-broadened HF with a general profile incorporating Dicke narrowing, speed-dependent broadening and shift, and collision-duration effects. Dicke narrowing is characterized by a combination of hard and soft velocity-changing collisions partially correlated with dephasing collisions. The various parameters affect the profiles with a unique pressure dependence and can be determined simultaneously using multispectrum fits. At measurement pressures below an atmosphere, the asymmetries are dominated by the Dicke correlations, with the speed-dependent shifts playing a secondary role. Here, the dispersive effects of collision duration are barely determinable and somewhat uncertain due to their sensitivity to the model.

We discuss spectral profiles from the point of view of a Boltzmann transport relaxation equation. We present an exact solution to the Fokker-Planck-type equation in the soft collision limit for the special case of a quadratic speed-dependent collisional width and shift of the line. The resultant spectral profile is compared to several related, more approximate expressions reported previously.

The octad system of methane (12)CH(4) has been analyzed with a fourth-order (459 parameters) Hamiltonian for energy levels and a third-order (28 parameters) dipole moment expansion for infrared intensities. Nearly 8000 assigned positions and 2500 measured line intensities (obtained with the Fourier transform spectrometer located at Kitt Peak National Observatory/National Solar Observatory) have been considered in the modeling. Infrared (Octad-Ground State) and hot bands (Octad-Dyad) data have been used. While the model does not reproduce the measurements at their inherent experimental precisions, it has been sufficient to interpret and substantially assign this spectral region of methane for the first time in over 30 years of investigation. Copyright 2001 Academic Press.

Speed-dependent broadenings and shifts have been determined for the P and R branches of the ν3 band of CH4 perturbed by Ar and N2 using a multispectrum fitting analysis of high-resolution tunable difference-frequency laser spectra recorded at pressures ≤67kPa. For J≥3, the tetrahedral fine structure components in each J manifold are collisionally coupled and exhibit significant interference. The coupled lines are treated using a speed-dependent first-order line-mixing profile and are compared to a speed-independent full relaxation matrix inversion procedure with off-diagonal coupling elements calculated from an atom–atom Lennard–Jones potential model.

Spectral profiles of overlapped lines are given for speed-dependent broadenings, shifts and couplings. Doppler broadening and Dicke narrowing are incorporated for analysis of atmospheric spectra. Dicke narrowing is treated in the hard velocity-changing collision limit both uncorrelated and correlated with phase- or state-changing collisions.

The analysis of the linestrengths of the infrared spectrum of methane (12 and 13) in the 3-5 µm region has been revisited on the basis of new measurements from Fourier transform spectra recorded at Kitt Peak under various optical densities. A simultaneous fit of these new data with previously reported tunable difference-frequency laser data has been done. An effective transition moment model in tensorial form up to the third order of approximation within the Pentad scheme has been used. The standard deviations achieved are very close to the experimental precision: 3 and 1.5%, respectively, for the two sets of data for the (12)CH(4) molecule, representing a substantial improvement with respect to earlier studies. The integrated bandstrengths obtained in the present work differ from previously reported values by factors ranging from -5 to +6%. The correction for the nu(3) band, the strongest band of the Pentad system, is +2% with respect to the study of Hilico et al. [J. C. Hilico, J. P. Champion, S. Toumi, V. G. Tyuterev, and S. A. Tashkun, J. Mol. Spectrosc. 168, 455-476 (1994)]. Copyright 2000 Academic Press.

Asymmetric line shapes observed for infrared transitions of Ar-broadened HF [A.S. Pine, J. Chem. Phys. 101, 3444 (1994)] were fit to Dicke-narrowed profiles with an empirical partial correlation between velocity- and phase-changing collisions. That analysis yielded measured broadening and shifting coefficients in excellent agreement with the thermally averaged values calculated by Green and Hutson [J. Chem. Phys. 100, 891 (1994)] from quantum close-coupled scattering cross-sections based on a realistic van der Waals potential. However, some anomalies in the sense of the asymmetries at low J and the magnitude and J dependence of the velocity-changing rates were noted, and are reexamined here by incorporating speed dependence into the collision parameters of the correlated Rautian profile. The speed dependence of the parameters is calculated from the reliable energy-dependent cross-sections of Green and Hutson. For HF/Ar below one atmosphere, we find that deviations from the conventional Voigt profile are dominated by correlated Dicke narrowing rather than speed-dependent effects, but the latter explain the anomalous asymmetries at low J.

The strong and sharp pQ3 subbranch of the ν7 band of ethane near 2976.8cm-1 is relatively free of interfering lines of methane, water and ozone and has been utilized as the signature of ethane for atmospheric monitoring. This subbranch is unresolvable at the Doppler limit, even at low temperature. However, the rotational structure and torsional splittings have been obtained by subDoppler molecular-beam spectroscopy, along with the air-broadening coefficients and their temperature dependence, so that the fundamental band subbranch can be well characterized, apart from minor perturbations evident at high J. This still leaves a significant fraction of the observed structure and intensity in this region unassigned. The strong temperature dependence of this extraneous structure enables us to attribute it to torsional hot bands, which improves the quantitative estimates of atmospheric ethane. We also discuss various approximations to the ethane partition function, accounting for the highly anharmonic torsional mode, needed for the accurate scaling of the intensities over the wide range of atmospheric temperatures.

Time series of CO and C2H6measurements have been derived from high‐resolution infrared solar spectra recorded in Lauder, New Zealand (45.0°S, 169.7°E, altitude 0.37 km), and at the U.S. National Solar Observatory (31.9°N, 111.6°W, altitude 2.09 km) on Kitt Peak. Lauder observations were obtained between July 1993 and November 1997, while the Kitt Peak measurements were recorded between May 1977 and December 1997. Both databases were analyzed with spectroscopic parameters that included significant improvements for C2H6relative to previous studies. Target CO and C2H6lines were selected to achieve similar vertical samplings based on averaging kernels. These calculations show that partial columns from layers extending from the surface to the mean tropopause and from the mean tropopause to 100 km are nearly independent. Retrievals based on a semiempirical application of the Rodgers optimal estimation technique are reported for the lower layer, which has a broad maximum in sensitivity in the upper troposphere. The Lauder CO and C2H6partial columns exhibit highly asymmetrical seasonal cycles with minima in austral autumn and sharp peaks in austral spring. The spring maxima are the result of tropical biomass burning emissions followed by deep convective vertical transport to the upper troposphere and long‐range horizontal transport. Significant year‐to‐year variations are observed for both CO and C2H6, but the measured trends, (+0.37±0.57)% yr−1and (−0.64±0.79)% yr−1, 1 sigma, respectively, indicate no significant long‐term changes. The Kitt Peak data also exhibit CO and C2H6seasonal variations in the lower layer with trends equal to (− 0.27±0.17)% yr−1and (−1.20±0.35)% yr−1, 1 sigma, respectively. Hence a decrease in the Kitt Peak tropospheric C2H6column has been detected, though the CO trend is not significant. Both measurement sets are compared with previous observations, reported trends, and three‐dimensional model calculations.

Intensities have been measured for individual transitions in the Q and R branches of the ν1 band of NH3 using a difference-frequency laser spectrometer. The data yield an integrated band strength of S0v=219.36±1.03 cm-2/MPa at 297 K, corresponding to a transition moment of ∣μv∣ = 8.535(20) × 10-32 C·m, and a Herman-Wallis correction factor, (1 + αjm)2, where αj = 0.0209(20). The intensities of a few lines for K ⩾ 7 were noticeably perturbed by a perpendicular Coriolis interaction with 2ν4 (E, l = 2), so were excluded from the fit. A small sample of ν3 band lines occurring in the ν1 band scans also yields a rough estimate of the ν3 band intensity with evident irregular perturbations.