1. Leicester lab study CAVIAR science meeting 10 th Feb 2011 (Cambridge Univ) Stephen Ball

2. Pulsed valve experiments Steve and Oliver (MChem project student) doing the lab work Equipment re-commissionned & working fine Nice BBCRDS spectra of bulk samples when chamber contains dilute water vapour Gas samples through slit valve built by M. Watkins Finding a water dimer signal will be a challenge – line the system up using a stronger absorber Water reservoir Pulsed valve LASER Carrier gas

3. Oxygen: pulsed valve + slit 10km 66cm 2.5 cm stdev(baseline) 5×10 –9 cm –1

4. Oxygen: pulsed valve + slit 10km 66cm 2.5 cm Molecules encountered per pass 2.7 × 760 Torr × 2.5 cm = 5130 Torr cm Molecules encountered per pass 21% × 93 Torr × 66 cm = 1290 Torr cm ×4

5. LASER Spring-loaded armature standard valve poppet pin hole orifice 1 1 30mm volume exchangeable slit (100 m 25mm) face plate Pulsed source needs to be aligned vertically, laterally & time sync with laser beam Ringdown time = 40 s LASER Translate left/right until bolt heads clip laser beam: optimum alignment is mid-point

6. Nitrogen dioxide: pulsed valve + slit 10km 66cm 2.5 cm stdev(baseline) 3×10 –9 cm –1

7. Where now with the Leicester work? Why arent we seeing strong absorbers through slit valve? Vertical & horizontal are OK – valve timing out of sync with laser beam? – sample gas not filling stagnation volume behind slit? Experiments on dilute bulk gases in cavity: 10 km path length through cavity low baseline noise on BBCRDS spectra dimer spectrum v wide at 750 nm so need cooling effect of pulsed source Continue experimental work we havent got to bottom of this yet! results for Olivers project report Realistic prospects of seeing the dimer in this exp?