D. Chris Benner

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

A MULTISPECTRUM NONLINEAR LEAST SQUARES FITTING TECHNIQUE

Abstract An extension of the nonlinear least squares spectrum fitting technique has been developed for the simultaneous fitting of multiple spectra. This procedures 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.

Methane line parameters in HITRAN

Abstract 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 6184.5 cm −1 ), but the database increased from 48,033 transitions in 2000 to 211,465 lines in 2001 because weaker transitions of 12 CH 4 and new bands of 13 CH 4 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.

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.

Methane and its isotopes: Current status and prospects for improvement

Abstract The compilations of molecular line parameters of methane are continually being updated and improved. In the present article, numerous changes made for the 1991 and 1992 versions of the HITRAN database in the 0–6185 cm-1 region are described. An assessment of the deficiencies in the parameters is also given.

Absolute intensity measurements of the (11 1 0) II ← 00 0 0 band of 12 C 16 O 2 at 5.2 μm

A nonlinear least-squares fitting procedure has been used to derive absolute intensities for lines in the P, R, and Q branches of the (1110)II ← 0000 band of 12C16O2 (band center = 1932 cm−1) from long-path 0.01-cm−1 resolution laboratory spectra. The spectral data were recorded at room temperature and low pressure (<10 Torr) with the Fourier transform spectrometer in the McMath solar telescope complex at Kitt Peak National Observatory. The observed line intensities were analyzed to derive the vibrational band intensity and F-factor coefficients. To obtain a good fit to the data, it was necessary to include terms in the expression for the F factor, which account for Coriolis-type and Fermi-type interactions and centrifugal distortion effects.

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.

Absolute line intensities in CO 2 bands near 4.8 μm

Absolute intensities have been determined for over 700 unblended lines in twenty bands of 12C16O2, 13C16O2, 16O12C18O, and 16O12C17O in the 4.8-μm spectral region. The spectral data used in the analysis were recorded at room temperature and low pressure (<10 Torr) with the Fourier transform interferometer in the McMath solar telescope complex of the National Solar Observatory. A natural sample of ultrahigh-purity carbon dioxide was used in the experiment. For each band, the measured line intensities have been fitted to derive the vibrational band intensity and coefficients of the F factor. These derived quantities are compared to values assumed in calculation of the 1982 Air Force Geophysics Laboratory line parameters compilation.

Measurements of 12 CH 4 ν 4 band halfwidths using a tunable diode laser system and a Fourier transform spectrometer

Air-broadened and N2-broadened halfwidths at room temperature for twenty-five transitions in the ν4 fundamental band of 12CH4 have been determined from IR absorption spectra recorded with a tunable diode laser spectrometer. Two tunable diode lasers operating in the 1250–1380-cm−1 region were used to obtain these data. Air-broadened halfwidths for twenty of these lines were also determined from additional spectra recorded at 0.01-cm−1 resolution with the Fourier transform spectrometer in the McMath solar telescope complex on Kitt Peak. The air-broadened halfwidths obtained from these two techniques are very consistent with agreement better than 3% in most cases.