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Theoretical work on the water monomer and dimer

Theoretical work on the water monomer and dimer. Matt Barber Jonathan Tennyson University College London 13 th May 2010 matt@theory.phys.ucl.ac.uk. Lab observations in the visible (broad band CRDS). For dimer spectroscopy Need accurate description of monomer contribution

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Theoretical work on the water monomer and dimer

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  1. Theoretical work on thewater monomer and dimer Matt Barber Jonathan Tennyson University College London 13th May 2010 matt@theory.phys.ucl.ac.uk

  2. Lab observations in the visible (broad band CRDS) For dimer spectroscopy Need accurate description of monomer contribution Including weak lines A.J.L. Shillings, S.M. Ball, M.J. Barber, J. Tennyson & R.L. Jones, Atmos. Chem. Phys. (to be submitted)

  3. Anomaly in HITRAN data from 8000 to 9500 cm-1

  4. Vibrational band intensities • Calculate from (perturbed) monomer vibrational wavefunctions • Requires Eckart embedding of axis frame • Use HBB 12 D dipole moment surface (DMS) corrected with accurate monomer DMS CVR: L. Lodi et al, J Chem Phys., 128, 044304 (2008) Issues: • PES used to generate monomer wavefunctions • (Cut) through 12 D DMS used

  5. Estimating transition frequencies Band centre from monomer DVR3D calculation Blue/red shift from calculation on perturbed PES Vibrational fine structure from dimer  dimer transitions

  6. Simulate spectra at “295 K” • Assume 4.5% dimer concentration • Rotational band profile 30 cm-1 (too narrow?) • Predictions give absolute intensities • 6D averaging But: Vibrational substructure still only for low T (8 J=0 states per symmetry) Results preliminary (main calculations in progress)

  7. Further Work Preliminary spectra for up to 10,000 cm-1 produced. Band profile comparisons show some encouraging signs. Effects of the sampling of the potential being investigated. Need all states up to dissociation Only 8 states per symmetry here It is a challenge for a much higher number of states Improved band origins coming soon

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