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Microwave

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by

Zachary Decker

on 28 January 2015

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Transcript of Microwave

Microwave Spectroscopy
What is Spectroscopy?
The study of light interacting with matter
Microwave - Rotational
1m-1mm
IR - Vibrational
1mm-650nm
UV/Visible - Electronic
650nm-10nm
Microwave Spectroscopy
Study of rotational transitions
Determine molecular structure
Identify molecules
How does it work?
Arbitrary Waveform Generator
Lowpass Filter
Filters out higher frequencies
Reflects or absorbs
Double Balanced Mixer
Mix
0-5Ghz (Arb) + 13.6Ghz PDRO
100 Mhz - 4900 Mhz
250ns
10 Gs/s
Chirp Pulse
Phase-locked Dielectric Resonator Oscillator
Bandpass Filter
Allows only certain frequencies
Specified Range
Bandpass Filter
Pre-amplifier
amplifies pulse to line level
0dBm
Solid State Amplifier
amplifies to ~43dBm
Single junction isolators
Prevents pulse from reflecting back
Wave Guide
Double Ridged
10 meters
Coiled
Diode Limiter
Fail safe
Above 21dBm
SPST Switch
Open-high attenuation
Closed-low attenuation
Low Noise Amplifier
~38dBm gain
Bandpass Filter
Double Balanced Mixer
Lowpass Filter
Intermediate Frequency Amplifier
15dBm increase
10,000 FIDs in ~1min
3 Main components
Wave Generator
Waveguide
Oscilloscope
Chirp pulse (polarization pulse)
Aligns rotating molecules
Applies a torque
Synchronous rotation
Emitting electric field
Electric field decays
Producing FID
FID is Fourier transformed
Free Induction Decay (FID)
Selecting Molecules
Stick to ~1 methyl rotor
Permanent dipole
High vapor pressure
Relatively small
Good Partition Function
Common Shipman Lab Expressions
"Flood the wave guide"
Floods the waveguide with molecule
"Pumping down"
Lowers the pressure inside the waveguide
"Bake out"
Cleans out the molecule by sucking at high temperatures
Taking Data
Find optimal pressure
Pump down while monitoring peak height
50 sets blank
High pressure
2x 50 sets data
Pump down to optimal pressure
Use robot to monitor pressure
50 set blank
Flood the wave guide
Repeat for each frequency range
Fitting Data
Find a "best fit line" for the theoretical spectrum
Use SVIEW to view actual data
Use ASCP to view theoretical data
Use SPCAT and S_View (Scripts) to calculate lines
Interstellar medium
Excited torsional states can tell about temperature
Temperature
Identification of interstellar weeds
Organic compounds dispersed in space
Importance of studying compounds with methyl rotors with low barriers to internal rotation
Different moments of inertia lead to different rotational spectra
Radio telescopes
Other applications
Atmospheric chemistry
Tropospheric ozone and isotopomers
Applications to Astrochemistry
Our Findings
First attempt was "scent of fear"
4-methyl-2pentanone
Failed
3 methyl rotors
Large
ASCP
SVIEW
Thank You
Shipman: Lab Space, Technical Advice, Espresso access, and being a
Fire Hose of Knowledge.

Maria: Our fearless leader

Bri: Our circuit encyclopedia
Our Findings
Second Attempt Nitromethane
Successful
1 methyl rotor
Good dipole
Puts out 13.6 Ghz
Overview
What is spectroscopy
How does it work
Circuit Setup
Selecting a molecule
Procedure of taking data
Fitting
Our Findings
Wave-Particle Duality
Light behaves like a wave and it behaves like a particle.
Full transcript