Kyle N. Crabtree, Carrie A. Kauffman, and Benjamin J. McCall 23 June 2009 McCall Research Group
Spectral taxonomy: A semi-automated combination of chirped- pulse and cavity Fourier transform...
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Transcript of Spectral taxonomy: A semi-automated combination of chirped- pulse and cavity Fourier transform...
![Page 1: Spectral taxonomy: A semi-automated combination of chirped- pulse and cavity Fourier transform microwave spectroscopy Kyle N. Crabtree, Marie A. Martin-Drumel,](https://reader036.fdocuments.net/reader036/viewer/2022062422/56649ec45503460f94bcf32c/html5/thumbnails/1.jpg)
Spectral taxonomy: A semi-automated combination of chirped-pulse and cavity Fourier transform microwave spectroscopyKyle N. Crabtree, Marie A. Martin-Drumel, and Michael C. McCarthy
Harvard-Smithsonian Center for Astrophysics
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Microwave spectroscopy at the CfA
Microwave spectroscopy of reactive molecules: astrochemistry, atmospheric chemistry, and exotic species
200 molecules detected in 20 yearsCations: HNNO+/NNOH+, H2NCO+
Anions: C4H-, C6H-, C8H-
Radicals: HOCO, HO3, C4H, HC3OExotic: Si3, HOON, CH2OO, HOCOH
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Cavity FTMspectrometer
Fourier transform spectrometer (5-26 GHz, 1 MHz bandwidth)
Supersonic expansion discharge nozzle
High sensitivity, high resolution
Dilutegaseous
precursors -HV
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CP-FTMW spectrometer
20 GHz, 50 GS/s scope
24 GS/sAWG
+38 dB
+30 dB
18.99 GHzPLDRO
10 MHz RbStandard
LPFilter
0.5-10.5 GHz;4 msec duration
StepAtten
0-70 dB
10 pulses; D 20 mst=0
t 250 ms
• Real-time phase scoring and correction• >1M co-averages routine
Linux DAQsoftware
18.5-8.5 GHz
200W7.5-18 GHz
TWTAData Validity
Monitor
Eccosorb−30 dB
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Opportunities and goals Chemical profiling of
reactive gas mixtures with intermediates (Miller-Urey-like experiments)
Conformer, vibrational-state discrimination
Analysis challenges for U-lines: Combine CP and cavity FT spectroscopy
Illustration by Adrian J. Hunter, CC-BY-SA 3.0
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Example: C2H2 + CS2 discharge150k gas pulses, 1.5M chirps: ~8.5h @ 5Hz1% C2H2, 1% C2S, 98% Ne1 kV discharge
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Example: C2H2 + CS2 discharge
495 features with SNR > 3 Of the strongest 34 features (SNR > 50):
13 artifacts (LO; harmonics; scope spurs) 10 assigned (C3S, c-C3H2, SO2, HC3S, C5S, H2C3S, C2S) 11 unidentified
150k gas pulses, 1.5M chirps: ~8.5h @ 5Hz1% C2H2, 1% C2S, 98% Ne1 kV discharge
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Chirped-pulse vs. cavityC
hir
ped
-pu
lse
8.5 h
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Chirped-pulse vs. cavityC
hir
ped
-pu
lse
Cavit
y
8.5 h
11 h
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Chirped-pulse vs. cavityC
hir
ped
-pu
lse
Cavit
y
8.5 h
11 h
8.5 h
9 s(0.0025 h)
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Chirped-pulse vs. cavityC
hir
ped
-pu
lse
Cavit
y
8.5 h
11 h
8.5 h
9 s(0.0025 h)
Bandwidth Intensity accuracy Resolution Frequency accuracy Sensitivity
Bandwidth Intensity accuracy Resolution Frequency accuracy Sensitivity
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Chirped-pulse + cavityC
hir
ped
-pu
lse
Cavit
y
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Chirped-pulse + cavityC
hir
ped
-pu
lse
Cavit
y
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Chirped-pulse + cavityC
hir
ped
-pu
lse
Cavit
y
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Automated analysis with cavity
QtFTM: Cavity control software designed for programmatic, automated acquisition
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Automated analysis with cavity
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Automated analysis with cavity Import list of
frequencies from CP spectrum
Automatically tune cavity to each frequency
Integrate for a duration based on CP intensity
Determine how many lines are present, fit to instrument response function
Remeasure under different conditions (e.g. discharge turned off)
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For each line found in CP spectrum, determine if line disappears when conditions change; classify:
Taxonometric classification
Discharge
Magneticfield
Gas 2present
Gas 1present
Buffer gasimpurities
Gas A cmplxor impurity
Gas
B c
mpl
x
or im
purit
y
Close
d-sh
ell
inte
rmed
/pro
d
Open-shell I/P
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Example acquisition: Discharge test
Dischargeenabled
Dischargedisabled
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Example acquisition: Discharge test
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Example acquisition: Discharge test
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Example acquisition: Discharge test
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Example acquisition: Discharge test
DC DC DC DC DC DC
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Taxonomy flowchart
Yes
Yes No
Yes No Yes No
Y N NY Y N Y N
Y N Y N Y N Y NY N Y N Y N Y N
Detected in cavity?
Discharge?
Magnetic?
CS2 only?
C2H2 only?
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Taxonomy flowchart
Yes
Yes No
Yes No Yes No
Y N NY Y N Y N
Y N Y N Y N Y NY N Y N Y N Y N
Detected in cavity?
Discharge?
Magnetic?
CS2 only?
C2H2 only?
795 1328 170 0 0 0 0 0 0 3 0 0 0
28 17 102 13 0 0 3 0
45 115 0 3
160 3
163
Non-detections: 330/495 (past expt: 20%)
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Taxonometric classification
Discharge
Magneticfield
C2H2
present
CS2
present0
0
0
00
00
395
7
132817
0
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Taxonometric classification
Discharge
Magneticfield
C2H2
present
CS2
present0
0
0
00
00
395
7
132817
0
Next step: cross-correlation within groups using double resonance
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MW-MW double resonance
fFTM
J = 0
J = 2
J = 1fFTM
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MW-MW double resonance
fDR
fFTM
J = 0
J = 2
J = 1fFTM
fDR
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MW-MW double resonance
fDR
fFTM
J = 0
J = 2
J = 1fFTM
fDR
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MW-MW double resonance
fDR
fFTM
J = 0
J = 2
J = 1fFTM
fDR
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DR cross correlation
Discharge
Magneticfield
C2H2
present
CS2
present0
0
0
00
00
395
7
132817
0
For each line, look for DR link at every other (unique) frequency# scans Nlines
2/2
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DR cross correlation – C2H2 magnetic
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DR cross correlation – C2H2 magnetic
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DR cross correlation – C2H2 magnetic
No DR
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DR cross correlation – C2H2 magnetic
Link!
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DR cross correlation – C2H2 magnetic
8/17 lines: c-C3H2
Remainder: unassigned.No obvious linkages
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DR cross correlation – C2H2 magnetic
8/17 lines: c-C3H2
Remainder: unassigned.No obvious linkages
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DR cross correlation
Discharge
Magneticfield
C2H2
present
CS2
present0
0
0
00
00
395
7
132818
0
Only the 60 strongest lines are shown in this example
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DR cross correlation – CS2 + C2H2 discharge
4: C5S4: C4S2: C3S n5=12: C3S n5=12: C13CCS
Remainder: unassigned.Some linkages are likely unassigned vibrational states of molecules above
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DR cross correlation – CS2 + C2H2 discharge
4: C5S4: C4S2: C3S n5=12: C3S n5=12: C13CCS
Remainder: unassigned.Some linkages are likely unassigned vibrational states of molecules above
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Spectral taxonomy
Future: 2-26 GHz CP coverage