J. Orphal

The 1997 spectroscopic GEISA databank

The current version GEISA-97 of the computer-accessible database system GEISA (Gestion et Etude des Informations Spectroscopiques Atmospheriques: Management and Study of Atmospheric Spectroscopic Information) is described. This catalogue contains 1,346,266 entries. These are spectroscopic parameters required to describe adequately the individual spectral lines belonging to 42 molecules (96 isotopic species) and located between 0 and 22,656 cm-1. The featured molecules are of interest in studies of the terrestrial as well as the other planetary atmospheres, especially those of the Giant Planets. GEISA-97 contains also a catalog of absorption cross-sections of molecules such as chlorofluorocarbons which exhibit unresolvable spectra. The modifications and improvements made to the earlier edition (GEISA-92) and the data management software are described. GEISA-97 and the associated management software are accessible from the ARA/LMD (Laboratoire de Meteorologie Dynamique du CNRS, France) web site: http://ara01.polytechnique.fr/registration.

The temperature and pressure dependence of the absorption cross-sections of NO2 in the 250-800 nm region measured by Fourier-transform spectroscopy

The absorption cross-sections of NO2 at atmospheric temperatures (223–293 K) and pressures (100 and 1000 mbar) were measured in the 250–800 nm (12500–40000 cm −1 ) region using Fourier-transform spectroscopy, at spectral resolutions of 0.5 cm −1 above 435 nm and 1.0 cm −1 below 435 nm (corresponding to about 8 and 16 pm at this wavelength). The wavenumber accuracy of the new cross-sections is better than 0.1 cm −1 (about 0.5 pm at 250 nm and about 6.4 pm at 800 nm), validated by recording of I2 absorption spectra in the visible using the same experimental set-up (light source, beam splitter, interferometer optics). The NO 2 absorption spectra were recorded at five different sample temperatures between 223 and 293 K, and at each temperature at two total pressures (100 and 1000 mbar) using pure N2 as buffer gas. Despite the weakness of this effect compared to the density of the NO2 absorption structures, pressure-broadening was clearly observed at all temperatures. The pressure-broadening was partially modeled using a convolution of the low-pressure NO2 absorption spectra with a Lorentzian lineshape. The pressure-broadening coefficient increases significantly with decreasing temperature, as already observed in the mid- and near-infrared vibration–rotation spectra of NO2. This effect is of importance for high-resolution spectroscopy of the earth’s atmosphere in the UV–visible region.

Ultraviolet and visible absorption cross-sections for HITRAN

Ultraviolet-visible absorption cross-sections are important reference data for remote sensing of atmospheric trace gases including O3; NO2; BrO; H2CO; OClO; SO2, and NO3 using optical instruments. In this paper, the reference absorption cross-sections for the HITRAN database are presented and needs for future improvements are addressed. ? 2003 Elsevier Ltd. All rights reserved.

FIRST OBSERVATION OF THE OIO MOLECULE BY TIME-RESOLVED FLASH PHOTOLYSIS ABSORPTION SPECTROSCOPY

Abstract In the time-resolved flash photolysis of I 2 in O 3 , in addition to the IO electronic bands between 21500 and 26000 cm −1 , a new absorption spectrum has been observed between 15000 and 21500 cm −1 , which is attributed to the A-X electronic bands of the OIO radical. A number of spectroscopic constants of the A state of OIO were determined by linear least-squares fitting the observed spectrum: ν 1 (symmetric IO stretch) ω 1 = 631 cm −1 , ν 1 anharmonicity constant ω 1 χ 1 = 2.6 cm −1 , ν 2 (OIO angle bend) ω 2 = 177 cm −1 , electronic energy with respect to the ground state T e = 14553 cm −1 . These values are in good agreement with those expected from measurements of the same electronic bands in OClO and OBrO.

Infrared synchrotron radiation: from the production to the spectroscopic and microscopic applications

Abstract This study reviews the various mechanisms exploited to produce infrared synchrotron radiation (IRSR). It shows that at long wavelengths (long when compared to the critical wavelength of the bending magnet in an electron storage ring), the radiation emitted from a bending magnet edge can be brighter than standard synchrotron radiation. For this purpose, we will discuss the various IRSR sources, namely the bending magnets, the wigglers, the undulator and the bending magnet edges. We will then briefly review a high-resolution study of isolated molecules in the far infrared, the detection of a very narrow Drude term in a high- T c superconductor, a description of ultra-high pressure experiments, an investigation of water encapsulated in non-ionic reverse micelles, and finally, a brief review of spatially resolved studies.

Fourier-transform cavity-enhanced absorption spectroscopy using an incoherent broadband light source

A cavity-enhanced absorption setup employing an incoherent broadband light source was used in combination with a Fourier-transform spectrometer to measure the spin-forbidden B-band of gaseous oxygen at approximately 688 nm and several weak absorption transitions of water vapor in the same spectral region at room temperature in ambient air. The experiments demonstrate that the sensitivity of a Fourier-transform spectrometer can be significantly improved by increasing the effective path length, while retaining a rather small sample volume. In comparison with a single-pass absorption measurement, we report a path-length enhancement factor of 200 and an improvement of the signal-to-noise ratio of approximately 6 in the present cavity-enhanced absorption experiment. The practical advantages and limitations of this novel approach are outlined and potential applications are briefly discussed.

High-resolution Fourier-transform cavity-enhanced absorption spectroscopy in the near-infrared using an incoherent broad-band light source.

An incoherent broad-band cavity-enhanced absorption (IBB-CEA) set-up was used in combination with a Fourier-transform (FT) spectrometer in order to explore the potential of this technique for high-resolution molecular spectroscopy in the near-infrared region. Absorption spectra of overtone bands of CO2, OCS, and HD18O were measured between 5800 and 7000 cm(-1) using a small sampling volume (1100 cm3, based on a 90 cm cavity length). The quality of the spectra in this study is comparable to that obtained with Fourier transform spectrometers employing standard multi-pass reflection cells, which require substantially larger sampling volumes. High-resolution methods such as FT-IBB-CEAS also provide an elegant way to determine effective mirror reflectivities (R(eff), i.e. a measure of the inherent overall cavity loss) by using a calibration gas with well-known line strengths. For narrow absorption features and non-congested spectra this approach does not even require a zero-absorption measurement with the empty cavity. Absolute cross-sections or line strengths of a target species can also be determined in one single measurement, if gas mixtures with known partial pressures are used. This feature of FT-IBB-CEAS reduces systematic errors significantly; it is illustrated based on CO2 as calibration gas.

Monitoring air quality from space: The case for the geostationary platform

Air quality (AQ) is defined by the atmospheric composition of gases and particulates near the Earths surface. This composition depends on local emissions of pollutants, chemistry, and transport processes; it is highly variable in space and time. Key lower-tropospheric pollutants include ozone, aerosols, and the ozone precursors NOx and volatile organic compounds. Information on the transport of pollutants is provided by carbon monoxide measurements. Air quality impacts human society, because high concentrations of pollutants can have adverse effects on human health; health costs attributable to AQ are high. The ability to monitor, forecast, and manage AQ is thus crucial for human society. In this paper we identify the observational requirements needed to undertake this task, discuss the advantages of the geostationary platform for monitoring AQ from space, and indicate important challenges to overcome. We present planned geostationary missions to monitor AQ in Europe, the United States, and Asia, and advocate for the usefulness of such a constellation in addition to the current global observing system of tropospheric compo

Vibrational progressions in the visible and near-ultraviolet absorption spectrum of ozone

Abstract In this Letter, we have recorded and analyzed new absorption spectra of ozone (215–2400 nm) at temperatures between 203 and 293 K. Two vibrational progressions have been identified in the visible part of the spectrum between 375 and 505 nm, leading to vibrational assignments, upper states vibrational frequencies and anharmonic coupling constants, and to an estimation of the vertical electronic energy of the 1 B 1 state, in overall agreement with recent theoretical predictions and with measurements of isotopic shifts at lower energies that were available in the literature.

Spectroscopic parameters for ozone and its isotopes: recent measurements, outstanding issues, and prospects for improvements to HITRAN

In this article we review ozone spectroscopy from the microwave to the ultraviolet since the release of the 1996 HITRAN database. Uncertainties, deficiencies, areas of potential improvement, and anticipated new spectral line parameters datasets are highlighted.