M. A. H. Smith

The hitran molecular database : editions of 1991 and 1992

Abstract We describe in this paper the modifications, improvements, and enhancements to the HITRAN molecular absorption database that have occurred in the two editions of 1991 and 1992. The current database includes line parameters for 31 species and their isotopomers that are significant for terrestrial atmospheric studies. This line-by-line portion of HITRAN presently contains about 709,000 transitions between 0 and 23,000 cm-1 and contains three molecules not present in earlier versions: COF2, SF6, and H2S. The HITRAN compilation has substantially more information on chlorofluorocarbons and other molecular species that exhibit dense spectra which are not amenable to line-by-line representation. The user access of the database has been advanced, and new media forms are now available for use on personal computers.

The HITRAN molecular spectroscopic database: edition of 2000 including updates through 2001

This paper describes the status circa 2001, of the HITRAN compilation that comprises the public edition available through 2001. The HITRAN compilation consists of several components useful for radiative transfer calculation codes: high-resolution spectroscopic parameters of molecules in the gas phase, absorption cross-sections for molecules with very dense spectral features, aerosol refractive indices, ultraviolet line-by-line parameters and absorption cross-sections, and associated database management software. The line-by-line portion of the database contains spectroscopic parameters for 38 molecules and their isotopologues and isotopomers suitable for calculating atmospheric transmission and radiance properties. Many more molecular species are presented in the infrared cross-section data than in the previous edition, especially the chlorofluorocarbons and their replacement gases. There is now sufficient representation so that quasi-quantitative simulations can be obtained with the standard radiance codes. In addition to the description and justification of new or modified data that have been incorporated since the last edition of HITRAN (1996), future modifications are indicated for cases considered to have a significant impact on remote-sensing experiments

The ν1 and ν3 bands of 16O3: Line positions and intensities

Abstract Using 0.005 cm −1 resolution Fourier transform spectra of samples of ozone, the ν 1 and ν 3 bands of 16 O 3 have been reanalyzed to obtain accurate line positions and an extended set of upper state rotational levels ( J up to 69, K a up to 20). Combined with the available microwave data, these upper state rotational levels were satisfactorily fitted using a Hamiltonian which takes explicitly into account the strong Coriolis interaction affecting the rotational levels of these two interacting states. In addition, 350 relative line intensities were measured from which the rotational expansions of the transition moment operators for the ν 1 and ν 3 states have been deduced. Finally, a complete listing of line positions, intensities, and lower state energies of the ν 1 and ν 3 bands of 16 O 3 has been generated.

Temperature dependence of broadening and shifts of methane lines in the ν4 band

Abstract We have recorded high-resolution absorption spectra of methane broadened by dry air and by N 2 at temperatures from −63 to 41°C using a Fourier transform spectrometer. These spectra have been analyzed to determine pressure broadening and line-shift coefficients, along with their temperature dependences, for 148 lines in the ν 4 fundamental band of 12 CH 4 . The experimental uncertainties for lines with J ″≤10 are generally b 0 L , 6–12% for its temperature dependence exponent n , 6–20% for the line-shift coefficient δ 0 , and 20–40% for its temperature dependence coefficient δ′; for J ″> 10 the experimental uncertainties are somewhat larger. These results, especially for N 2 -broadening, are in excellent agreement with other recent measurements. Since the present results cover a wide range of rotational quantum numbers ( J ″ up to 14), the variation of the temperature dependence of the half-widths and shifts from line to line within the ν 4 band is also examined.

The Hybrid-Type Bands ν1 and ν3 of 16O 16O 17O Line Positions and Intensities

Abstract A study of 0.005 cm −1 resolution room temperature absorption spectra of 17 O-enriched ozone around 10 μm has been performed leading to a thorough analysis of the hybrid ν 1 and ν 3 bands of 16 O 16 O 17 O. The experimental rotational levels af the interacting states (001) and (100) were reproduced using a Hamiltonian taking fully into account the rovibratianal interactions. Precise vibrational energies and rotational and coupling constants were deduced and the following band centers were determined: ν 0 (ν 1 ) = 1095.69309 cm −1 and ν 0 (ν 3 ) = 1035.35869 cm −1 . Using the 16 O 17 O 16 O line intensities calculated previously and assuming a factor of 2 between the abundances of 16 O 16 O 17 O and 16 O 17 O 16 O, the amount of 16 O 16 O 17 O in the cell was evaluated and used to derive the line intensities for this latter species. Then the experimental intensities were least squares fitted, leading to the determination of the transition moment constants of the ν 1 and ν 3 bands of 16 O 16 O 17 O. Finally a complete spectrum of these bands has been computed.

Measurements of the HCN ν3 band broadened by N2

Abstract N 2 -broadened halfwidths have been measured for 51 absorption lines belonging to the ν 3 fundamental band of hydrogen cyanide ( 1 H 12 C 14 N) near 3311 cm −1 . The data were recorded at room temperature using a Fourier transform spectrometer with a nominal resolution of 0.06 cm −1 . A nonlinear least-squares spectral-fitting procedure was used to obtain both line intensities and collision-broadened halfwidths from scans recorded at several different pressures. The N 2 -broadened halfwidths, determined for all lines with J ≤ 25 in both the P and R branches of the band, show the expected distribution with J for broadening by a nonpolar gas. The halfwidth values range from approximately 0.17 cm −1 atm −1 near the band center to 0.11 cm −1 atm −1 for high- J lines. The band intensity for the ν 3 fundamental derived from these measurements is 236.2 ± 9.5 cm −2 atm −1 at 296 K, and empirical coefficients for the vibration-rotation interaction F -factor were also determined.

Line positions and intensities for the ν1 + ν2 and ν2 + ν3 bands of H218O

Abstract The intensities of about 90 lines of the ν 1 + ν 2 and ν 2 + ν 3 bands of H 2 18 O have been measured using a Fourier transform spectrum of natural water vapor. The constants involved in the rotational expansion of the transformed transition moment operators corresponding to these bands have been determined through a fit of these line intensities. The constants obtained are used to compute the whole spectrum of the ν 1 + ν 2 and ν 2 + ν 3 bands of H 2 18 O providing reliable line positions and intensities. For lines involving perturbed levels a comparison is given with the results obtained for H 2 16 O and it is shown that the results for one isotopic species cannot be transferred directly to another one.

Tunable diode laser measurements of N2- and air-broadened halfwidths: Lines in the (ν4 + ν5)0 band of 12C2H2 near 7.4 μm

Abstract Nitrogen- and air-broadened Lorentz halfwidths have been determined for 29 lines in the P and R branches of the (ν4 + ν5)0 combination band of 12C2H2 using a tunable diode laser spectrometer. Two tunable diode lasers operating in the region 1250–1380 cm−1 were used in recording the data. For nitrogen broadening, the measured halfwidths at 296 K decrease from about 0.11 cm−1 atm−1 at |m| = 1 to about 0.05 cm−1 atm−1 at |m| = 30, where m = J″ + 1 for R-branch lines, m = −J″ for P-branch lines, and J″ is the lower state rotational quantum number. On the average, the air-broadened halfwidths are 97% of the N2-broadened halfwidths.

Sensitivity of ozone retrievals in limb-viewing experiments to errors in line-width parameters

The variance of atmospheric ozone concentration profiles retrieved in i.r. limb-viewing experiments is examined over the range of published ozone halfwidth values. Simulated retrievals are performed for a typical satellite-based high-resolution absorption experiment and a broad-band emission experiment. The results indicate that, for limb-viewing experiments, inaccurate collision-broadened linewidth values can lead to significant errors in retrieved profiles for broad-band radiometric data or for isolated strong lines in high-resolution spectra.

Line parameters for 16O3 bands in the 7-μm region

Abstract Lines of the very weak 2 ν 2 and ν 1 + ν 3 − ν 2 bands of 16 O 3 have been identified in the region 1370 to 1440 cm −1 of 0.01 cm −1 resolution solar occulatation spectra of the stratosphere. The spectral data were acquired from orbit by the atmospheric trace molecule spectroscopy (ATMOS) Fourier transform spectrometer during the Spacelab 3 shuttle mission. Initial assignments for the lines were obtained by using positions calculated from accurate molecular constants derived in recent high-resolution laboratory studies. From these results and spectral simulations of the interfering atmospheric absorptions, 59 16 O 3 lines in the atmospheric spectra were selected for intensity measurements using the equivalent width technique. Precise transition moment constants for both bands were then deduced from the measured intensities and used with the molecular constants to generate a complete listing of line positions, intensities, and lower state energies useful for atmospheric applications. The integrated band intensities in units of cm −1 /molecule cm −2 at 296 K are 5.43 × 10 −22 for the 2 ν 2 band and 1.01 × 10 −21 for the ν 1 + ν 3 − ν 2 band.