Instrumental Analysis amp Initial Molecular Results Nathan Seifert Wolfgang Jäger University of Alberta Nearly 10 Years of Broadband Rotational Spectroscopy ID: 661197
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Slide1
A New 2.0-6.0 GHz Chirped-Pulse Fourier Transform Microwave (CP-FTMW) Spectrometer:
Instrumental Analysis & Initial Molecular Results
Nathan Seifert
, Wolfgang
Jäger
University of AlbertaSlide2
(Nearly) 10 Years of Broadband Rotational Spectroscopy
2008: First instrument paper published in
Rev Sci
Instrum
Now:
G. B. Park, R. W. Field,
J. Chem. Phys.
2016
, 144, 200901.
Many groups around the world with chirped pulse instrumentation!
Molecular structure
UAlberta
,
Umanitoba
(RF08), U Virginia (WG07)
Max Planck CFEL (next talk!)
,
E Illinois Univ. (RH04),
Amherst College (RA02), Wesleyan University (TC02),
Universidad de Valladolid (WC05), Universidad de
Pais
Vasco (TH04),
and more!!!
Reaction Kinetics
MIT, Missouri (MI02), Argonne Nat. Lab. (WH02)
Astrochemically
-Relevant Molecular Species
Harvard (RA03), UC Davis (WE11), Koln (TH08)
Analytical
Chemistry
(e.g. Head space analysis)
Brightspec
, LLC (WE09, WG10)Slide3
CP-FTMW Spectroscopy at
UofA
Current CP-FTMW Spectrometer: Example Measurement
100 MHz – 1 GHz
1-4 µs chirped pulse
12.0 GHz CW
11.0 – 11.9 GHz
12.1 – 13.0 GHz
25 W solid state amplifier
Low noise
high gain amplifier
13.5 GHz CW
Molecular signal, 11-13 GHz
500 MHz – 2.5 GHz
High speed digitizer
Arbitrary waveform generator
Doppler limited; T
2
ca. 5 µs
Free induction decay
Fourier transformSlide4
CP-FTMW Spectroscopy at
UofA
Current CP-FTMW Spectrometer: Primary Bottlenecks
Low noise
high gain amplifier
Molecular signal, 11-13 GHz
High speed digitizer
Arbitrary waveform generator
Limited bandwidth:
Requires frequency
synthesizer as local
oscillator to cover entire band
Low power
25 W amplifier limits
sensitivity;
generally scales as P
1/2
up to
> 500 W
Slow data processing:
Collecting FIDs a slow process
-- practically limits repetition
rate to ca. 1 Hz
Spectral impurities
Mixing artifacts derived from
synthesizer’s spurious signals
intense enough to require
background subtraction
Room for improvement everywhere!Slide5
2.0-6.0 GHz CP-FTMW design
Arbitrary waveform generator
High speed digitizer
1-3 GHz
1-8 µs chirped pulse
x2
+15
dBm
-15
dBm
2-6 GHz
+46
dBm
6.1 GHz
phase-locked oscillator
Low noise
amplifier
0.1-4.1 GHz
Improved bandwidth:
Only
doubler
required to
reach required band;
can output up to 4.8 GHz
for direct measurements
Improved power:
Approximately 2x power
relative to previous
generation CP-FTMW
instrument
Improved gain:
Higher directionality/ gain
antennae and improved low
noise amplifier improve
molecular signal detection
Cleaner heterodyning:
PLO has order of magnitude
improvements in spectral
purity relative to synthesizers
Higher speed digitization:
Significant improvements over
Previous gen digitizer at
UofA
.
At 20 µs detection length, 25Gs/s
6 frames per valve pulse --- effective
maximum rate is 10Hz.
Low-compression switch:
High power-handling SPDT
switch (RF Lambda) used to
reduce CW noise power and
limit compression of pulseSlide6
Initial Results:
ortho-dichlorobenzene
Frequency (MHz)
Amplitude (mV)
2
12
- 1
11
35
Cl /
37
Cl
35
Cl /
37
Cl
2
02
- 1
01
Expt., 7k average (10 min)
Revised prediction (new constants)
FWHM: 75 kHz
Value / MHz
Onda
& Yamaguchi
[1]
New
A
1930.02(13)
1930.26(34)
B
1431.16(7)
1432.73(24)C
821.670(4)821.15(79)1.5χ
aa-56.9(20) -61.90(88)
0.25(χ
bb -χcc )
-6.0(13)-6.11(20)
χ
ab---55.3(51)
/ 48.3(47)RMS
0.1340.009
[1] M. Onda, I. Yamaguchi, J. Mol. Struct.
1976, 34, 1-7.Slide7
Methyl Lactate Comparison
Amplitude (mV)
Frequency (MHz)
1
01
-0
00
S/N: ~8000:1 @ 730k
avg
8000:1 @ 730k average
11.3:1 @ 1
acqusition
Or, at 2 Hz (12
acq
/s)
39:1 @ 1 second
3
03
-2
02
S/N (
): 170:1 @ 2000
avg
170:1 @ 2000 average
4:1 @ 1
acqusition
Or, at 0.5 Hz (3
acq
/s)
7:1 @ 1 second
2-6 GHz CP-FTMW
8-18 GHz CP-FTMW, after fixes
Power (arb units)
Frequency (MHz)
At face value, the new chirp is winning by a bit, BUT….
Intrinsic intensity (log
10 scale) @ Trot = 2 K:
101-000 : -3.55
3
03-202 : -2.27
Therefore, the 3
03 is intrinsically 19
times more intenseAt equivalent performance to the new chirp, the 303
– 202 should be 740:1 @ 1 second.Slide8
Deep Averaging: (2-fluoroethanol)
4
3.0-4.5 GHz, 1.34 million averages
0.1% 2-fluoroethanol, 3
atm
He
Frequency (MHz)
Intensity (µV)
9
18
-8
26
6
15
-5
05
6
24
-5
14
New tetramer detection!
Experiment
B3LYP-D3/6-311++g(
d,p
)
A / MHz
561.19622(96)
558.7
B
289.3763(17)
303.0
C
250.0267(20)
262.8
D
J
/ kHz
0.070(3)
D
JK-0.035(2)
N /
σ
/ kHz18 / 7.3Slide9
Future Goals & Plans
LABVIEW-free spectrometer control software
VISA-compliant suite written in full Python
Laser Ablation
Heated sample reservoir & gas nozzle
Promising initial results with a number of test molecules
MW-MW Double Resonance & other
multiresonant
pulse sequences
Easy to program with current-generation AWGs
(D)- (left) / (L)- (right) tartaric acid,
addition and insertion based
monohydrates
Only possible with laser ablation!
(
mp
. 172 °C)
First significant study completed thanks to new instrument:
(trifluoroethanol)
3
(see RG06!)
Traveling wave tube amplification coming soon
2-8 GHz, ~400 W
One step ahead of us!
Alonso group from Valladolid reports on
monomer tomorrow (
WC05
)Slide10
Thank you!
Acknowledgements
Yunjie
Xu,
Javix
Thomas
Mohamad al-
Jabiri
Elijah Schnitzler, David
LoewenChemistry Dept. Machine Shop