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1 Water vapour self-continuum: Recent interpretation Igor Ptashnik, Keith Shine, Andrey Vigasin University of Reading (UK) Zuev Institute of Atmospheric Optics (Russia) Institute of General Physics (Russia) Lab & Theory CAVIAR meeting 30.04.2010 UCL, London Slide 2 2 Water continuum and water dimers (1600-8000 cm -1 ) The "problem of the third peak" Slide 3 3 Water continuum and water dimers (1600-8000 cm -1 ) Metastable dimers are expected to produce similar to "smoothed" H 2 O spectral features Slide 4 4 Water continuum and uncertainty in H 2 O line parameters In 1600 cm -1 band: 50 to 100% systematic error in H 2 O line para- meters is required to explain the deviation from MTCKD. In 3600 cm -1 band: 100 to 300% systematic error in strongest H 2 O lines' parameters would be required to explain deviation from MTCKD There cant be up to 100-200% deviation from Lorentzian profile in WM lines within just 1-3 cm -1 from the line centres at these pressures! (It is not far wings) Slide 5 5 Bimolecular absorption. Partitioning of pairs in the phase space Bimolecular absorption can be formally split in three parts: Free-pair collisions (or CIA), caused by single-collision induced (or changed) dipole moment; True bound (stable) dimers; and Quasibound (metastable) dimers. The "water continuum question" then is: Which parts of BA contribute most to the continuum? The answer depends on intermolecular potential and temperature, and has been demonstrated for a few molecular pairs ( O 2 -O 2, CO 2 - CO 2, N 2 -N 2, H 2 O-H 2 O ) on the basis of statistical partitioning of the molecular pairs in the phase space (Vigasin, Kluwer-2003). Slide 6