Transcript 2010_Columbus_h2o.ppt

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.
Herschel-HIFI (Heterodyne Instrument for the Far-IR)
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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
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Water spectroscopy
• C2V symmetry, 11,000 cm-1 barrier to linearity
– Bond angle changes a lot (many degrees) even in pure rotation
– Bigger change upon exciting n2 mode
• Stretching slightly more rigid than bending but not much
• Watson Hamiltonian does not converge!
– DKK4>AK2 at J~10
– DJ and (B+C)/2 are not much better
– Series in J(J+1) and K2 alternate in sign
• Spectrum extremely difficult to extrapolate
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Water spectroscopy-Strong coupling
000
IF
010
IF
IF
IC
020
SF
SC
100
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.
001
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Project Goals
• 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 2n2
• Measure weak and high J GS and n2 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)
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Experiments at JPL
H2O
Beamsplitter
Pump
Sample cell
Rooftop
reflector
Si detector
Lock-in
PC
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3
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2
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6 FM
Discharge
Multiplier chain
Rf Synthesizer
Source frequency: 300–1230, 1575–1626 GHz
H2O: 30 mTorr
DC discharge: 400 mA, ~3 kV
Discharge cell: 1.2-meter-long
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Experiments at Cologne
• Frequency range
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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
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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
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Examples of hot water spectra
1(1,0)-1(0,1) transitions
n3 at 524 GHz
n1 at 540 GHz
2n2 at 793 GHz
GS at 557 GHz; n2 at 658 GHz
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High K ground state
108,3 – 99,0 and 108,2 – 99,1
119,3 – 1010,0 and 119,2 – 1010,1
Calculated position of 1010 is off by a few MHz
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Laboratory spectrum!?
020 66,1-75,2
Absorption peak is up with our phase convention!
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Simple optically pumped maser
21,2
20,2
1753 GHz
maser
11,0
658 GHz
maser
899 GHz
11,1
n2 State
1205 GHz maser
10,1
00,0
6 micro optical pumping
20,2
21,2
1669 GHz
11,0
557 GHz
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Ortho
988 GHz
11,1
Ground
State
1113 GHz
10,1
00,0
Para
Excited water
Summary of observed H2O transitions
• 145 pure rotational transitions in its GS, n2, 2n2, n1 and n3
– 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, n1, n3, but missing for n2 (1753914
GHz), 2n2 (1872972 GHz)
– 1(1,1)-0(0,0) observed for GS, n2, n1, n3 but missing for 2n2
(1332967 GHz)
• Observed highest J
– 18 for GS (E = 4174 cm-1)
– 14 observed for n2 (E = 4174 cm-1)
– 9 observed for 2n2 (E = 4774 cm-1)
– 6 for n1 (E = 4381 cm-1)
– 5 for n3 (E = 4126 cm-1)
• About 10 transitions between 500–580 GHz to be measured at JPL
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Fitting water spectra with Euler series
Euler series obtained by transforming the angular momentum operators
Pickett et al, 2005
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Euler series
D1,0 = A
D0,1 = (B+C)/2
d0,0 = (B-C)/2
Pickett et al, 2005
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Euler series success
• H2O ground state and n2 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
• D2O (Köln & JPL)
– Analyzed ground and n2 to reduced RMS of 1.6
• CH2 (Köln ~2003)
• Key is to get a clean data set and choose ‘av’ and ‘bv’
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Status of H2O 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!
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Coping with nonconvergance
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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
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A closer look
001 State
020 State
Larger Moment to ground
4658.97471
74,4
Small moment to ground
4812.19276
77,0
4407.04635
66,1
4368.63692
75,2
4197.33874
65,2
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Perturbation
4491.36973
64,2
4452.35271
72,6
4408.02880
63,3
4345.27202
4350.69931
54,2
62,4
4050.50370
55,0
4165.47381
52,4
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