David A. Newnham

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

Integrated absorption intensity and Einstein coefficients for the O2 a 1Δg–X 3Σg− (0,0) transition: A comparison of cavity ringdown and high resolution Fourier transform spectroscopy with a long-path absorption cell

The two experimental techniques of cavity ringdown spectroscopy and high-resolution, long-path Fourier transform spectroscopy have been used to measure quantitative absorption spectra and determine the integrated absorption intensity (Sint,B) for the O2 au200a1Δg–Xu200a3Σg− (0,0) band. Einstein A-factors and radiative lifetimes for the O2 au200a1Δg v=0 state have been derived from the Sint,B values. The two methods give values for the integrated absorption intensity that agree to within 2%. The value recommended from the results of this study is Sint,B=3.10±0.10×10−24u200acmu200amolecule−1, corresponding to an Einstein-A coefficient of A=2.19±0.07×10−4u200as−1 and a radiative lifetime of τrad=76u200amin. The measurements are in excellent agreement with the recent absorption study of Lafferty et al. [Appl. Opt. 37, 2264 (1998)] and greatly reduce the uncertainty in these parameters, for which accurate values are required for determination of upper stratospheric and mesospheric ozone concentrations.

Visible absorption cross sections and integrated absorption intensities of molecular oxygen (O2 and O4)

Absorption spectra of gas-phase molecular oxygen and zero air at temperatures of 223 and 283 K have been measured in the laboratory using a coolable multipass-optics gas cell and Fourier transform spectroscopy in the wavelength range 455 to 830 nm (12,000-22,000 cm -1 ). Net absorption cross sections of the O 2 A-, B-, and γ-bands at <0.002 nm spectral resolution, and pressures of 100 and 1000 hPa zero air have been determined. Binary absorption cross sections of the collision-induced O 4 bands at <0.18 nm spectral resolution and a pressure of 1000 hPa pure oxygen have been determined, with corrections for the O 2 γ-band absorption. Calculated integrated absorption intensities and, for the O 2 A- and B-bands, effective Einstein A-coefficients are compared with previous literature values.

Highly sensitive detection of trace gases using the time-resolved frequency downchirp from pulsed quantum-cascade lasers

A spectrometer using a pulsed, 10.25-μm-wavelength, thermoelectrically cooled quantum-cascade distributed-feedback laser has been developed for sensitive high-resolution infrared absorption spectroscopy. This spectrometer is based upon the use of the almost linear frequency downchirp of up to 75 GHz produced by a square current drive pulse. The behavior of this downchirp has been investigated in detail using high-resolution Fourier-transform spectrometers. The downchirp spectrometer provides a real-time display of the spectral fingerprint of molecular gases over a wave-number range of up to 2.5 cm-1. Using an astigmatic Herriott cell with a maximum path length of 101 m and a 5-kHz pulse repetition rate with 12-s averaging, absorption lines having an absorbance of less than 0.01 (an absorption of less than 1%) may be measured.

New studies of the visible and near‐infrared absorption by water vapour and some problems with the HITRAN database

New laboratory measurements and theoretical calculations of integrated line intensities for water vapour bands in the near-infrared and visible (8500–15800 cm−1) are summarised. Band intensities derived from the new measured data show a systematic 6 to 26% increase compared to calculations using the HITRAN-96 database. The recent corrections to the HITRAN database [Giver et al., J. Quant. Spectrosc. Radiat. Transfer, 66, 101–105, 2000] do not remove these discrepancies and the differences change to 6 to 38%. The new data is expected to substantially increase the calculated absorption of solar energy due to water vapour in climate models based on the HITRAN database.

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.

Infrared band strengths and absorption cross-sections of HFC-32 vapour

Abstract Infrared absorbance cross-sections and integrated band strengths for HFC-32 (difluoromethane, CH 2 F 2 ) vapour have been determined from laboratory measurements at eight temperatures (203, 212, 222, 243, 253, 264, 287, and 297 K) for the region 600–1900 cm −1 at 0.03 cm −1 instrument resolution, by Fourier transform infrared spectroscopy. In addition, air-broadened spectra of HFC-32 vapour have been recorded at 203, 251, and 297 K at pressures of 5, 20, and 100 kPa air.

VUV and low energy electron impact study of electronic state spectroscopy of CF3I

Abstract The electronic states of CF3I have been investigated using photon and electron energy loss spectroscopy from 4 to 20xa0eV (310xa0nm>λ>60xa0nm). Assignments have been suggested for each of the observed absorption bands incorporating both valence and Rydberg transitions. Vibrational structure in each of these bands is observed for the first time. Absolute photo-absorption cross-sections have also been measured and are compared with earlier measurements.

Fourier transform infrared spectroscopy of HCFC-142b vapour

Abstract Infrared absorbance cross sections and integrated band strengths for HCFC-142b (1-chloro-1,1-difluoroethane, CH 3 CC1F 2 ) vapour have been determined at six temperatures (203, 213, 233, 253, 273 and 294 K) for the region 600–1500 cm −1 by Fourier transform infrared spectroscopy. Air-broadened spectra of HCFC-142b vapour have been recorded at 203, 253 and 294 K using mixtures containing 5, 20 and 100 kPa dry air. Spectroscopic resolution was 0.03 cm −1 , with additional high resolution (0.002 cm −1 ) measurements of the pure vapour at 203 and 294 K.

INFRARED ABSORPTION CROSS-SECTIONS AND INTEGRATED ABSORPTION INTENSITIES OF HFC-134 AND HFC-143A VAPOUR

Abstract Infrared absorption cross-sections and integrated absorption intensities of HFC-134 (1,1,2,2-tetrafluoroethane) and HFC-143a (1,1,1-trifluoroethane) vapour have been determined from laboratory measurements at six temperatures (203, 213, 233, 253, 273 and 297 K) for the region 560–1900 cm −1 (5.3–17.9 μm) at 0.03 cm −1 instrument resolution, by Fourier transform infrared spectroscopy. In addition, air-broadened spectra have been recorded at 297 K and pressures of 5, 20 and 100 kPa air. Inter-comparisons between this work and previous studies have been made where possible.