Project Details:
Intensities and line shapes in high-resolution spectra of water isotopologues from experiment and theory
| Project No.: | 2011-022-2-100 |
| Start date: | 2012-01-01 |
| End date: | 0000-00-00 |
| Division: | Physical and Biophysical Chemistry Division |
A previous IUPAC Task Group (#2004-035-1-100), overlapped with members of the present one, completed the critical compilation and theoretical verification of accurate experimental line positions and energy levels for the major water isotopologues. The compiled comprehensive database is crucial for a wide range of scientific applications.
Hereby we propose to extend this effort and plan to determine accurate line intensities, line widths, and pressure effect spectral parameters of water vapor, including again its major isotopologues. The proposed analyses will be undertaken based on newly developed experimental and theoretical tools. Intensities and pressure-broadened line shapes for several water isotopologues form the missing information for understanding the complete spectroscopy of water isotopologues. The joint experimental and theoretical results will be published in the open literature and all the spectroscopic parameters determined will be placed in relevant databases freely available to the public.
Water is arguably the single most important molecule. It is ubiquitous in the Universe, fundamental to life on Earth, is one of the dominant greenhouse gases, and is a major product of combustion processes. Therefore, detailed characterization of the complete spectrum of water vapor is important in many fields of chemistry, physics, and engineering. Water vapor is responsible for about 70 % of the known absorption of sunlight and the majority of the greenhouse effect and line-by-line simulations require accurate data. While knowledge of accurate line positions determined by energy levels and selection rules is a necessary prerequisite for modelers, in many applications temperature-dependent line intensities and lineshapes are just as important. Solar, planetary and exoplanetary astronomy and astrophysics make extensive use of water column density information, which again requires detailed and accurate knowledge of intensity and lineshape information. The accurate data needed can only be provided by a joint experimental and theoretical investigation, as proposed here. It is our belief that several of the applications will fail to advance without accurate linelist information for at least a few key molecular species, such as water isotopologues.
Spectra of water vapor in different regions of the electromagnetic radiation reveal important facts about the quantum dynamics of the triatomic water molecule. This information is highly relevant not only in scientific but also in engineering applications. Measurements result in a large amount of data about line positions and energy levels. While this information is usually accurate, it is far from being complete, as revealed by the analyses of the previous TG on water spectroscopy.
The present collaborative effort is aimed at devising and constructing a huge database comprising, eventually, the complete linelist information for all major isotopologues of water vapor in a form applicable for studies at all temperatures (from ultracold to ultrahot). To achieve this ambitious goal this project brings together researchers (chemists, physicists, computer scientists, and spectroscopists) from all over the world who are active in studying the fine details of the rovibrational spectra of water as well as IT experts knowledgeable about data handling. The previous TG on water spectroscopy identified the shape of line profiles (currently largely Voigt) as a subject for urgent attention. Recommending and implementing a line profile for water is a major issue for the new task group: two new members (Lisak and Tran) who are experts in this area have been invited to join the TG.
Extending efforts of a previous IUPAC TG (JQSRT 2009, 110, 573 and 2010, 111, 2160), the proposed collaboration aims at determining line intensities (via Einstein A coefficients), line shapes, and pressure effects parameters for all major isotopologues of water. There is no hope for a complete experimental characterization of the rovibrational spectra of water isotopologues under hot and cold conditions, not least because hot applications require the characterization of up to a billion transitions per isotopologue. There exists no complete and accurate theoretical model with which one can predict the complete high-resolution spectrum of water with an accuracy required by the numerous applications. Nevertheless, unlike transition wavenumbers, computed intensities are often more accurate than but the best experimental values. Consequently, only a judicious combination of experiment and theory will lead to a complete understanding of the spectroscopy of water vapor.
To augment the presently available results a concerted effort including both high-quality experiments to characterize the shapes of the lines of the spectra of water and its isotopologues (using Laser Absorption Spectroscopy, Cavity-Ring Down Spectroscopy, Cavity Enhanced Absorption Spectroscopy, etc.) at a number of wavelengths and temperatures and new theoretical methods of computing intensities and shapes are needed. One particular difficulty to be addressed is the theoretical evaluation of the temperature dependence of spectroscopic parameters, vitally important for modeling purposes.