Transcript Ka Band.pptx

A Ka-Band Chirped-Pulse Fourier Transform Microwave
Spectrometer
DANIEL P. ZALESKI, JUSTIN L. NEILL, MATTHEW T. MUCKLE
AND BROOKS H. PATE
Department of Chemistry, University of Virginia, McCormick Rd., P.O. Box 400319,
Charlottesville, VA 22904
P. BRANDON CARROLL AND SUSANNA L. WIDICUS WEAVER
Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, GA 30322
Centers for Chemical Innovation
The Ohio State 65th International Symposium on Molecular Spectroscopy, June 22nd, 2010.
Introduction to Ka-Band
http://www.nrao.edu/index.php/learn/vlavc
Ka-Band is 26 – 40 GHz
builds on technological advances in the arbitrary waveform
generation for telecommunications
Interested in driving chirped-pulse up in frequency
Robert Field – MIT
Chirped-Pulse Millimeter-Wave (CPmmW) Spectrometer
operates at 70 – 84 GHz or 87 - 102 GHz
Kevin Douglass - NIST
en.wikipedia.org:Geremia
PROGRESS TOWARDS CHIRPED-PULSE
FOURIER TRANSFORM THZ SPECTROSCOPY
WH09 3:36 2015 McPHERSON
Many astronomical species have transitions in this region
creation and detection of short-lived non-terrestrial species (e.g. ions and radicals)
GBT and E/VLA overlap – enhanced chemical imaging capabilities
Park, G. B., Steeves, A. H., Kuyanov-Prozument, K., Colombo, A. P., and Field, R. W. Design and Chemical Application of Chirped-Pulse Millimeter-Wave
(CPmmW) Spectroscopy. The 64th Ohio State International Symposium on Molecular Spectroscopy. June 25, 2009.
25 – 40 GHz CP-FTMW Spectrometer
Primary concern is presence of spurious signals and
“ghosts”
Ghosts can occupy a large number of detection channels
for a dense spectrum
Main ghosts that remain come from mixing off twice the
PDRO frequency
Ultimately use a 44 GHz PDRO to mix down
Gordon G. Brown, Brian C. Dian, Kevin O. Douglass, Scott M. Geyer, Steven
T. Shipman, and Brooks H. Pate. Rev. Sci. Instrum. 79, 053103, (2008).
Time-Frequency Analysis of the Chirped-Pulse
Before entering the TWT
Mostly a multiplier problem – putting out x3 and x4
Can see the other side band but it is mostly suppressed – in principle it could be filtered
OCS Benchmarking – Dynamic Range
Dynamic range was tested using the spectrum of OCS
Yields reliable relative intensities across orders of magnitude, evidenced by isotopic intensity ratios
The detection of the O13C33S isotopomer (0.0076% terrestrial abundance) demonstrates this dynamic range
Accurate relative intensities allow relative species populations and relative dipole moments to be derived
OCS Natural Abundance Measurements – Relative Intensities
NIST
Isotopomer
J=3-2
O-C-S
Broadband
Frequency (MHz) Abundance
Frequency (MHz)
Abundance % Difference
36488.813(3)
93.74
36488.802
O-C-34S
35596.91(3)
4.158
35596.862
4.9850
19.89%
O-13C-S
36371.390(30)
1.053
36371.392
1.2315
16.95%
36022.424
36027.902
36027.902
36029.706
36029.707
36033.102
36035.179
0.74
0.03035
0.11899
0.07437
0.1821
0.26559
0.03885
0.02974
36022.414
0.0348
14.52%
36027.896
0.1548
-19.93%
36029.700
36033.090
36035.172
0.4083
0.0282
0.0282
-8.80%
-27.29%
-5.20%
O-C-S
34229.045(30)
0.188
34229.016
0.2815
49.71%
O-13C-34S
35470.264(20)
0.0467
35470.258
0.0387
-17.16%
O-C-S
35301.903
0.035
35301.924
0.0190
-45.79%
O-C-36S
34798.022
0.0167
34798.026
0.0184
10.09%
18
O-C-34S
33359.691
0.00834
33359.698
0.0091
8.55%
O-13C-33S
35905.78
35907.586
0.00107
0.00253
35905.786
35907.594
0.0021
0.0023
100.78%
8.73%
18
34146.273
0.00211
34146.282
0.0034
61.13%
O-C-33S
F=7/2-7/2
F=5/2-3/2
F=3/2-1/2
F=7/2-5/2
F=9/2-7/2
F=5/2-5/2
F=3/2-3/2
18
17
O-13C-S
Total
27.64%
6 – 18 GHz BB
18.60%
F. J. Lovas and R. D. Suenram. J. Chem. Phys. 87, 2010-2020, (1987).
Gordon G. Brown, Brian C. Dian, Kevin O. Douglass, Scott M. Geyer, Steven T.
Shipman, and Brooks H. Pate. Rev. Sci. Instrum. 79, 053103, (2008).
OCS Natural Abundance Measurements – Relative Intensities
NIST
Isotopomer
J=3-2
O-C-S
Broadband
Frequency (MHz) Abundance
Frequency (MHz)
Abundance % Difference
36488.813(3)
93.74
36488.802
O-C-34S
35596.91(3)
4.158
35596.862
4.9850
19.89%
O-13C-S
36371.390(30)
1.053
36371.392
1.2315
16.95%
36022.424
36027.902
36027.902
36029.706
36029.707
36033.102
36035.179
0.74
0.03035
0.11899
0.07437
0.1821
0.26559
0.03885
0.02974
36022.414
0.0348
14.52%
36027.896
0.1548
-19.93%
36029.700
36033.090
36035.172
0.4083
0.0282
0.0282
-8.80%
-27.29%
-5.20%
O-C-S
34229.045(30)
0.188
34229.016
0.2815
49.71%
O-13C-34S
35470.264(20)
0.0467
35470.258
0.0387
-17.16%
O-C-S
35301.903
0.035
35301.924
0.0190
-45.79%
O-C-36S
34798.022
0.0167
34798.026
0.0184
10.09%
18
O-C-34S
33359.691
0.00834
33359.698
0.0091
8.55%
O-13C-33S
35905.78
35907.586
0.00107
0.00253
35905.786
35907.594
0.0021
0.0023
100.78%
8.73%
18
34146.273
0.00211
34146.282
0.0034
61.13%
O-C-33S
F=7/2-7/2
F=5/2-3/2
F=3/2-1/2
F=7/2-5/2
F=9/2-7/2
F=5/2-5/2
F=3/2-3/2
18
17
O-13C-S
Total
27.64%
6 – 18 GHz BB
18.60%
Not listed in
Lovas
catalog
F. J. Lovas and R. D. Suenram. J. Chem. Phys. 87, 2010-2020, (1987).
Gordon G. Brown, Brian C. Dian, Kevin O. Douglass, Scott M. Geyer, Steven T.
Shipman, and Brooks H. Pate. Rev. Sci. Instrum. 79, 053103, (2008).
OCS Benchmarking – Optimum Polarizing Power
Red line – weak pulse limit
To optimally polarize a lot more power is needed
Ethyl Formate
1 Riveros
2
and Wilson. J. Chem. Phys. 46, 4605, (1967).
A. Belloche. et al. A&A, 499, 215, (2009).
LABORATORY DETECTION OF THE TRANSGAUCHE CONFORMER OF ETHYL FORMATE
TJ15 5:41 2015 McPHERSON
Ethyl formate has three possible conformations
The cis-trans and cis-gauche conformers are lowest in energy 1
Discovery of the cis-trans conformer in the interstellar medium has recently been reported 2
The rotational spectrum of the third conformer has been obtained
Two Lowest Energy Conformers of Ethyl Formate
ethyl formate (97% purity, Sigma-Aldrich) 0.2% concentration with Ne
gas was expanded through a General Valve Series 9 nozzle with 1 mm diameter - backing
pressure of 15 psi
the nozzle pulse duration was 700 µs - repetition rate of 0.8 Hz
817,000 FIDs were collected - total measurement time of 28 h (run consecutively)
S/N on strongest line is 40,000:1
25 - 40 GHz/6 - 18 GHz Comparison
The noise levels of the two spectra are scaled to their relative number of signal averages and nozzles
These are compared to simulated spectra (SPCAT)
The sensitivity of the 25 - 40 GHz spectrometer compares favorably to the 6 - 18 GHz spectrometer
- even though the TWTA power is lower by a factor of approximately 4
Smaller spot size resulting in a larger field - well matched to where the molecules are, more directional
Ethyl Formate Substitution Structures
large circles: ab initio structure
small circles: substitution coordinates
cis ester-trans ethyl (above left)
cis-gauche (below left)
(below right)
Stark Effect
The cage is a voltage divider – many small
voltage drops rather than a single large one
Expansion is unaffected and the nozzle is in a low
voltage region
Two high voltage power supplies are needed
+ and –
Simultaneous dipole measurements on multiple
species
Efficient Stark fits for each species
Emilsson, T., Gutowsky, H. S., de Oliveira, G., Dykstra, C. E. J. Chem. Phys. 112, 1287, (2000).
Stark Effect – TFP Calibrator
J=6-5
Lit:
Exp:
2.317 D
2.319(18) D
StdDev ~ 80 KHz
Confident
parameters
in
zero-field
Only fitting to 1 parameter
Need to be revisited
Kasten, W., Dreizler, H. Z. Naturforsch. A, 39, 1003, (1984).
Harder H., Gerke C., Mader H., Cosleaou J., Bocquet R., Demaison J., Papousek D., and Sarka K. J. Mol. Spec., 167, 24, (1994).
Stark Effect – Ethyl Formate Low Energy Conformers
J=7-6
Lit:
Exp:
a = 1.85 D
b = 0.69 D
a = 1.879(97) D b = 0.746(25) D
J=4-3
Lit:
Exp
a = 1.44 D
b = 1.05 D
c = 0.25 D
a = 1.458(41) D b = 1.069(49) c = 0.182(19) D
J. M. Riveros and E. B. Wilson. J. Chem. Phys. 46, 4605, (1967).
Expected Upgrades
New oscilloscope (first half 2011)
 Improvements to fast frame
 Increase signal acquisition by about a factor of 10
80+ GS/s scope in the near future?
 allow for direct detect at 40 GHz
 requires some oversampling
 Agilent Technologies produces a 32 GHz scope
filter for the 44 GHz PDRO
Acknowledgements
Current Members of The Pate Lab
Matt Muckle
Justin Neill
Amanda Steber
Collaborators
S. Spezzano, V. Lattanzi, and M. C. McCarthy
Harvard-Smithsonian Center for Astrophysics, and School of
Engineering and Applied Sciences, Harvard University
Centers for Chemical Innovation
Award Number 0847919