1 CAVIAR science meeting 29 th Sept 2010 (National Physical Laboratory) Stephen Ball Leicester University

Submitted to Atmospheric Chemistry & Physics: 2 nd August Editor assigned: 24 th August Editors report: 26 th August Manuscript + minor revisions submitted: 13 th Sept Accepted for discussion: 19 th Sept Production files submitted: 27 th Sept Type setting manuscript / galley proof / publication as an online discussion paper… 2

3 Result 1: The UCL_08 line list does a better job of fitting the water monomer structure than HITRAN08 Result 2: No evidence of a dimer feature like Pfeilstickers in the BBCRDS residual.…. but there might be something if the dimer band is very wide Result 3: Dimer band would have to be extremely wide (HWHM > 100 cm -1 ) for any signal lurking in the BBCRDS residual to be consistent with (i) K eq and (ii) theoretical line strengths K eq ??

4 Where is the Leicester work now? Leicester CAVIAR post-docs contract ended 30 th April SMB back in the lab this summer? – some apparatus improvements, but no new experiments. Dual heater around pulsed nozzle; Slit design 10,000 cavity passes The baseline noise on BBCRDS spectra of water monomer at low pressures demonstrate detection system is operating as well as for the Shillings et al study.

5 Is it worth continuing? Shillings et al (exp) & Garden et al 2008 (theory) suggest that dimer bands around 750 nm will be very broad: difficult to observe in experiments under equilibrium conditions requires non-equilibrium cooled experiments: the many dimer transitions that merge to form a wide feature at room temp now cooled to a series of narrower resolvable bands? The hardware is in good shape; the apparatus is still available. MChem 4 th year project student – recruited: SMB back in the lab next semester! Kuyanov-Prozument