1. Terahertz spectroscopy of excited water Shanshan Yu, John Pearson, Brian Drouin Jet Propulsion Laboratory, California Institute of Technology, USA Adam Walters Centre d'Etude Spatialedes Rayonnements, Universite de Toulouse, France Holger Müller and Sandra Brünken I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany Copyright 2010 California Institute of Technology. Government sponsorship acknowledged.

2. Excited water Shanshan Yu Herschel-HIFI (Heterodyne Instrument for the Far-IR) ESA and NASA joint mission Launch: 2009 (3 years lifetime) Telescope: 3.5 meter diameter, <100 K temperature The only space facility dedicated to the terahertz part of the spectrum Spectral coverage: 1910–1410 GHz; 1250–480 GHz Objectives: life cycle of gas and dust

3. Water spectroscopy Shanshan Yu Excited water C 2V symmetry, 11,000 cm -1 barrier to linearity –Bond angle changes a lot (many degrees) even in pure rotation –Bigger change upon exciting 2 mode Stretching slightly more rigid than bending but not much Watson Hamiltonian does not converge! –D K K 4 >AK 2 at J~10 –D J and (B+C)/2 are not much better –Series in J(J+1) and K 2 alternate in sign Spectrum extremely difficult to extrapolate

4. Excited water Shanshan Yu 000 010 020 100 001 IF SF IC SC IF= Isolated Fermi Resonance IC= Isolated Coriolis Resonance SF=Strong Fermi Resonance SC=Strong Coriolis Resonance Note that this is limited to J=25. Water spectroscopy-Strong coupling

5. Project Goals Excited water Shanshan Yu Measure transitions to Ortho GS 1(1,0)-1(0,1) & 2(1,2)-1(0,1) –1(1,0)-1(0,1) is done –2(1,2)-1(0,1) remains to be done Measure transitions to Para GS 1(1,1)-0(0,0) –1(1,1)-0(0,0) done except for 2 2 Measure weak and high J GS and 2 transitions Measure other low lying triad transitions Check accuracy of previous measurements –Some surprises in previous microwave measurements Critically reviewing and fitting the lowest 5 states –previous reduced RMS of 8.4 (some known calibration issues)

6. Experiments at JPL H 2 O: 30 mTorr DC discharge: 400 mA, ~3 kV Discharge H2OH2O Sample cell Pump Beamsplitter Rooftop reflector FM Rf Synthesizer Multiplier chain PC Si detector Lock-in ×6×6 ×2×2 ×3×3 … Source frequency: 300–1230, 1575–1626 GHz Discharge cell: 1.2-meter-long Excited water Shanshan Yu

7. Experiments at Cologne Frequency range –290–968 GHz with BWOs; –1.42–1.45 THz with a VDI multiplier chain; –1.85–1.99 THz with a sideband spectrometer Numerous ways to generate hot water –RF-discharge (200 W, ~2 m); –DC discharge (~2 kV, ~300 mA and 1.5 m); –A pyrolysis oven (~1500 K and 50 cm absorption path); –Heating tape (~450 K and 3.5 m) Pressures: 10–50 mTorr Detector: a composite InSb bolometer cooled with liquid He Excited water Shanshan Yu

8. Excited water Shanshan Yu Examples of hot water spectra GS at 557 GHz; 2 at 658 GHz 3 at 524 GHz 1 at 540 GHz  2 at 793 GHz 1(1,0)-1(0,1) transitions

9. Excited water Shanshan Yu High K ground state 11 9,3 – 10 10,0 and 11 9,2 – 10 10,1 Calculated position of 10 10 is off by a few MHz 10 8,3 – 9 9,0 and 10 8,2 – 9 9,1

10. Laboratory spectrum!? Absorption peak is up with our phase convention! 020 6 6,1 -7 5,2 Excited water Shanshan Yu

11. Simple optically pumped maser 1 0,1 1 1,0 2 1,2 1669 GHz 557 GHz 0 0,0 1 1,1 2 0,2 1 0,1 1 1,0 2 1,2 1753 GHz 658 GHz maser 1113 GHz 6 micro optical pumping 988 GHz 0 0,0 1 1,1 2 0,2 1205 GHz maser 899 GHz Ground State 2 State Ortho Para Excited water Shanshan Yu

12. Summary of observed H 2 O transitions 145 pure rotational transitions in its GS, 2, 2 2, 1 and 3 –Frequency range: 293 – 1969 GHz –86 are new transitions –1(1,0)-1(0,1) observed for all the five states –2(1,2)-1(0,1) observed for GS, 1, 3, but missing for 2 (1753914 GHz), 2 2 (1872972 GHz) –1(1,1)-0(0,0) observed for GS, 2, 1, 3 but missing for 2 2 (1332967 GHz) Observed highest J –18 for GS (E = 4174 cm -1 ) –14 observed for 2 (E = 4174 cm -1 ) –9 observed for 2 2 (E = 4774 cm -1 ) –6 for 1 (E = 4381 cm -1 ) –5 for 3 (E = 4126 cm -1 ) About 10 transitions between 500–580 GHz to be measured at JPL Excited water Shanshan Yu

13. Fitting water spectra with Euler series Euler series obtained by transforming the angular momentum operators Excited water Shanshan Yu Pickett et al, 2005

14. Euler series Excited water Shanshan Yu D 1,0 = A D 0,1 = (B+C)/2 d 0,0 = (B-C)/2 Pickett et al, 2005

15. Excited water Shanshan Yu Euler series success H 2 O ground state and 2 to J=22 (JPL 2001) –Subsequent TUFIR measurements agreed with in error bars –One high J line was off 3 MHz all others <1 MHz –Reduced RMS 1.9 –Found a number of suspicious assignments in IR data D 2 O (Köln & JPL) –Analyzed ground and 2 to reduced RMS of 1.6 CH 2 (Köln ~2003) Key is to get a clean data set and choose ‘a v ’ and ‘b v ’

16. Excited water Shanshan Yu Status of H 2 O data analysis Reviewing the lowest 5 states IR data in progress –Experimental uncertainty underestimated? –Calibration factor? –Bad measurements and blends? –Misassignments? Thanks for your attention!

17. Excited water Shanshan Yu

18. Excited water Many approaches developed over the years – Padé Approximates (Burenin) – Borel Approximates (Polyansky) – Generating function in K (Tyuterev & Starikov) – Euler Series (Pickett) – Adjustable Bending potential (Coudert) – Full spectroscopic potential (Partridge & Schwenke; Tennyson, Polyansky & Zobov) Best for all levels is the full potential empirically adjusted by the observed spectrum – Still not to experimental accuracy (factor of a few for IR) – Not suitable for microwave transitions due to insufficient accuracy Euler series works and is in SPFIT – Fitted approach works can predict microwave transitions Coping with nonconvergance

19. A closer look 6 6,1 7 5,2 7 7,0 5 5,0 6 5,2 6 3,3 4408.02880 4350.69931 6 2,4 4491.36973 6 4,2 7 2,6 7 4,4 4658.97471 4452.35271 5 4,2 5 2,4 4345.27202 4165.47381 4050.50370 4407.04635 4197.33874 4368.63692 4812.19276 020 State Small moment to ground 001 State Larger Moment to ground Perturbation Excited water Shanshan Yu