Theoretical work on the water monomer and dimer Matt Barber Jonathan Tennyson University College London 13 th May 2010

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)

Anomaly in HITRAN data from 8000 to 9500 cm -1

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, (2008) Issues: PES used to generate monomer wavefunctions (Cut) through 12 D DMS used

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

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)

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