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Physical and Biophysical Chemistry Division (I)


Number: 2004-035-1-100

Title: A database of water transitions from experiment and theory

Task Group
: Jonathan Tennyson (TCHV)

Members: Peter Bernath (ECH) , Alain Campargue (ECH), Michel R. Carleer (ECH), Attila G. Császár (T), Robert Gamache (TL), Joseph Hodges (ESVL), Alain Jenouvrier (EC), Olga Naumenko (TCH), Oleg Polyansky (TCHD), Larry Rothman (DVL), Robert A. Toth (EC), Ann Carine Vandaele (EC), and Nikolai Zobov (TCH)

Field of expertise of the individual as related to the project, whereby E = experimentalist, T = theoretician, C = cold water spectra, H = hot water spectra, D = data handling, V = data validation, S = standardization, and L = line profiles

Critical compilation, experimental determination and validation, and theoretical verification and extension of accurate frequency, energy level, line intensity, line width, and pressure effect spectral parameters of water and all of its major isotopologues.

The full characterization of the spectrum of water vapor from the microwave to the near ultraviolet is a prerequisite for modeling and understanding of many fields in chemistry, physics and engineering, including (1) atmospheric modeling, with emphasis on the definitive understanding of global warming (water vapor is responsible for about 70 % of the known atmospheric absorption of sunlight and the majority of the greenhouse effect), (2) communication-related fields using the Earth's atmosphere, such as satellites and telecommunication, (3) astronomy, such as that of cool stars (where hot water is a major constituent), (3) water lasers and masers, widespread in outer space, (5) study of comets, based on fluorescence spectroscopy, and (6) combustion research, such as rocket exhausts, forest fires, and turbine engines (hot steam is a major product of most combustion processes).

Water spectra have been the subject of immense scientific effort resulting in a large number of data. They are used mostly without critical evaluation, comparison, and inclusion in annotated databases, an exception being the (room temperature) HITRAN database.

The present collaborative effort is aimed at devising and constructing a database comprising, eventually, the complete linelist of all major isotopologues of water for studies at all temperatures. To achieve this goal this project will bring together researchers from around the globe who are active in studying the rovibrational spectra of water as well as experts in related data handling. The linelist to be compiled will include theoretical and (where available) experimental values of transition frequencies, intensities, and pressure broadening parameters for all major isotopologues. Emphasis will be on validation, comparisons, and test of the database.

Despite a huge effort by experimentalists in the past, a breakthrough and an essential improvement in this field may not be expected in the foreseeable future. There is no hope for a complete experimental characterization of the rovibrational spectra of water isotopologues under hot and cold condition, not least because hot applications require the characterization of up to a billion transitions. Similarly, despite significant progress in the area (see, e.g., Polyansky et al., Science 2003, 299, 539), there exists no complete and accurate theoretical model with which one can predict the high-resolution spectrum of water. Consequently, only a judicious combination of experiment and theory will lead to an understanding of the spectroscopy of water, which is arguably the single most important polyatomic molecule.

Knowledge of the spectral and temperature dependence of the water vapor continuum is important for modeling atmospheric radiative balances. The continuum can be measured using high-sensitivity techniques, such as cavity ring-down spectroscopy. Calculations based upon existing DBs usually substantially underestimate the continuum cross sections, a situation which is to be remedied here.

The first compilation of rovibrational levels of H216O was published recently by members of this Task Group (Tennyson et al., J. Phys. Chem. Ref. Data 2001, 30, 735) proving the feasibility of such an undertaking by a thoughtful combination of experimental and theoretical procedures.

To augment the presently available results a concerted effort including both high-quality experiments to characterize the spectra of water and its isotopologues (using Fourier Transform Spectroscopy, Laser Absorption Spectroscopy, Cavity Ring-Down Spectroscopy, Cavity Enhanced Absorption Spectroscopy, etc., coupled with the use of state-of-the-art techniques for water vapor sample preparation) at a number of wavelengths and temperatures and new theoretical calculations of spectra, based on variational treatments are needed. One particular difficulty to be addressed is the theoretical evaluation of pressure and temperature dependence of spectroscopic line profiles, vitally important for modeling purposes.

To achieve the stated goals of this project requires a concerted effort of experimental and theoretical chemists and physicists, spectroscopists, and computer scientists.


Last update: 3 February 2005

<project announcement to be published in Chem. Int.>


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