Number: 2004-035-1-100
Title: A database of water transitions from
experiment and theory
Task Group
Chairman: 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
Objective:
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.
Description:
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.