J. Vander Auwera

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

Vibrational Spectroscopic Database on Acetylene, X̃ 1Σg+(12C2H2,12C2D2, and 13C2H2)

Information on the vibrational energy states in acetylene (12C2H2, 12C2D2, and 13C2H2) is gathered: spectroscopic constants (vibrational frequencies and anharmonicities, vibration-rotation interaction parameters), observed vibrational energy states and complete sets of predicted vibrational energies and predicted principal rotational constants Bv for states of 12C2H2, 12C2D2, and 13C2H2 up to 15000, 10000, and 12000 cm−1, respectively. Statistical parameters (partition functions and integrated number of states) deduced from these predicted spectroscopic data are provided for the three isotopomers. The equilibrium geometrical structure is determined to be re(CH)=106.138(35) pm and re(CC)=120.292(13) pm from constants available for 12C2H2, 12C2D2, 13C2H2, and 12C2HD.

Toward an Accurate Database for the 12 μm Region of the Ethane Spectrum

The ν9 fundamental band of ethane occurs in the 12 μm region. It is the strongest band of ethane in a terrestrial window in the thermal infrared and is commonly used to determine ethanes abundance in the atmospheres of the Jovian planets and comets and to determine their temperature. Precise and accurate absolute intensities of this band are crucial for correct interpretation of recent Cassini observations of ethane spectra in the atmospheres of Saturn and Titan, as well as of Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) observations in the terrestrial atmosphere. Using a spectrum of the ν9 band of ethane recorded at 278 K at the Pacific Northwest National Laboratory, we show that the line parameters available in the HITRAN and GEISA databases do not allow reproduction of the experimental data to within their accuracy. In fact, the integrated band intensity calculated at 296 K using both line lists are, respectively, a factor 1.57 larger and 1.44 smaller than the observed value. Using results from a recent global analysis of data involving the four lowest vibrational states of ethane and measurements of pressure-broadening parameters, we generate a new set of line parameters which we show to provide a much more accurate description of the experimental spectrum of C2H6 in the 12 μm region.

L-type resonances in C2H2

A full Hamiltonian matrix coherent with a phase convention leading to e/f labellings and to positive l-doubling q parameters is constructed to describe the rovibrational energy levels in a linear polyatomic molecule with two bending vibrations. This model is used to investigate quantitatively the effect of the rotational and vibrational l resonances on level mixings and intensity features in C2H2.

The IR acetylene spectrum in HITRAN: update and new results

The 2000 HITRAN edition, with the updates of 2001, contains improved and new data on the acetylene molecule. The main changes concern the 13.6- and 7.5-μm spectral regions (improved line intensities), and the 5-μm region (previously absent from the database). These changes are reviewed, and the key problem of the validation of line intensities is dealt with. The status of the currently available line parameters is critically examined, and recommendations for future improvements are given.

An intercomparison of laboratory measurements of absorption cross-sections and integrated absorption intensities for HCFC-22

Abstract An intercomparison of measurements of infra-red absorption cross-sections and integrated absorption intensities in HCFC-22 has been carried out. Independent measurements were made by five spectroscopy groups so that their experimental methods and data reduction techniques could be critically examined. The initial results showed a spread in reported values for integrated absorption intensity over the mid infra-red spectral region that were larger than the reported uncertainties. Re-examination of experimental and data reduction methods resulted in consistency of results within the reported errors. It was found that particular attention had to be paid to controlling and characterising errors associated with the non-linear response of MCT detectors and pre-amplifiers, adsorption of the sample on surfaces in the absorption cell, effectiveness of mixing when making measurements on mixtures of absorber gas and a buffer gas, and location of the photometric “full-scale” and “zero” levels.

Laser spectroscopy of the ν1+3ν3 absorption band in 12C2H2. I. Pressure broadening and absolute line intensity measurements

We have developed a Ti:Sa autoscan laser spectrometer and used it to perform a detailed investigation of individual line profiles in the ν1+3ν3 band of 12C2H2. Pressure self-broadening effects were measured for most lines with J″ values ranging from 0 to 22, and for pressures between 10 and 600 Torr. The high-pressure data points (p>250 Torr) are fitted satisfactorily by a Voigt profile. Line narrowing, characterized by an underestimation of the Lorentz contribution to the Voigt profile, was observed for the low pressures range (p<150 Torr), indicating the influence of molecular confinement. The two usual limit models (soft and hard collisions) were fitted to the observed line shapes in order to extract more precise information concerning the pressure broadening. The present results confirm the absence of strong vibrational dependence in the self-broadening coefficients. Absolute line intensities are also determined in the fitting procedure. No significant differences were found for the two pressure domai...

Overtone spectroscopy of formic acid

Abstract Vibrational assignments of fundamental, combination and overtone bands in the main isotopomer of gaseous trans-formic acid are reported from spectra either newly or previously [J. Chem. Phys. 113 (2000) 1535] recorded using high-resolution Fourier transform and intracavity laser absorption spectroscopies. A total of 62 bands, with 32 newly reported ones, are observed from the lowest energy band, ν7 at 626.16 cm−1 up to 4ν1 at 13284.1 cm−1. Among these bands, 43 are firmly assigned, and 16 tentatively. Effective vibrational constants are obtained. The normal modes of vibrations are further characterised using ab initio calculations providing fundamental band intensities and picturing normal mode nuclear displacements. The effective investigation of the rotational structure in the first CH stretch overtone band (2ν2) and in the second OH stretch overtone band (3ν1) is detailed. Rotational information is also presented for 3ν2 and two close-lying bands, that could be extracted from the strong overlapping formic acid dimer bands using artificial filtering procedures.

High-resolution investigation of the far-infrared spectrum of formic acid

Abstract We have analyzed the pure rotation spectrum of formic acid, recorded in the far infrared in the range from 20 to 130 cm −1 using a Bruker IFS120HR Fourier transform spectrometer. A list of calculated lines positions from 10 to 100 cm −1 and of corresponding predicted absolute intensities has been created.

Absolute line wavenumbers in the near infrared: 12C2H2 and 12C16O2

40 absolute line wavenumbers in the 3v 3 band of 12C16O2 between 6927 cm−1 and 6989 cm−1 and 626 absolute line wavenumbers in the near infrared absorption spectrum of 12C2H2 between 7060 cm−1 and 9900 cm−1 have been measured using high resolution Fourier transform spectroscopy. The calibration of the CO2 line wavenumbers relied on heterodyne frequencies available in the v 1 + v 3 band of 12C2H2 near 6556 cm−1. The absolute uncertainty of the calibrated CO2 line wavenumbers is estimated to 0.000 08 cm−1. The acetylene spectra were calibrated using heterodyne frequencies available in the 2—0 band of 12C16O and the line wavenumbers obtained in the 3v 3 band of 12C16O2. The absolute uncertainty of the calibrated acetylene line wavenumbers is estimated to range from 0.0003 cm−1 to 0.006 cm−1 for strong to very weak isolated lines. Comparison with absolute line wavenumbers obtained independently at JPL in the 3v 3 band of 12C2H2 near 9649 cm−1, calibrated using absolute wavenumbers available in the 2—0 and 3—0 (near 6350 cm−1) bands of 12C16O, shows very good agreement. Also, the vibration—rotation constants for the observed upper vibrational states of 12C2H2 were determined, but without accounting for the perturbations affecting these states.