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TE021
Pressure Broadening and Spectral Overlap in the Millimeter Wave Spectrum of Ozone
International Symposium on Molecular Spectroscopy
65th Meeting — June 21–25, 2010
6/22/2010
Corey Casto and Frank C. De Lucia
The Ohio State University
TE022
Introduction
6/22/2010
Millimeter region:172-262 GHz
Atmospherically broadened lines Van Vleck-Weisskopf
line profile P = 100 – 760 torr FWHM = 0.5 – 4.6 GHz Significant overlap Isolated lines?
TE023
Experiment
6/22/2010
Cavity characteristics
3 second scan ~6000
resonances in the 172 – 262 GHz range
FSR = 14.5 MHz Q ~ 7 106
Ringdown = 1/c ~ 5 s
Quasi-OpticalIsolator
InSbDetector
DAQPulse
Generator
BWO HVPower
10.3 m
TE024
Low Pressure
6/22/2010
Good agreement between model and experiment
Intensities and linewidths are consistent Residual is not significantly greater at the
peaks Lines are isolated and less prone to mixing
effects
TE026
Causes of error near line peaks
6/22/2010
Intensity Frequency Experiment Linewidth Line Mixing
TE027
Residuals at various pressures
6/22/2010
Ozone concentration is constant~ 150 ppm
Narrow features are consistent
Broad features increase by an order of magnitude
TE028
Causes of error near line peaks
6/22/2010
Intensity Frequency Experiment Linewidth Line Mixing
TE029
Global linewidth adjustment fit
6/22/2010
= g ga(T0/T)na
ga Air-broadened linewidth in MHz/torr
na Air-broadened coefficient of temperature dependence
Overlap makes measurement of linewidths difficult
Global fit prevents pressure dependent parameters
TE0210
Global Fit Linewidth Adjustments
6/22/2010
Disagreement is <5% for most lines
Many lines are known to within 2-5%
How does this affect residuals?
TE0211
Residuals with global fit parameters
6/22/2010
Low pressure residuals don’t increase High pressure residuals improve near line
centers Linewidth error is not sufficient to explain
residual Published parameters accurately describe
our data
TE0212
Causes of error near line peaks
6/22/2010
Intensity Frequency Experiment Linewidth Line Mixing
TE0213
Line mixing characteristics
6/22/2010
Lines not isolated Inelastic collisions allow
coupling of lines First order effects can be
expressed in a modified line profile
Wing skewing Small center shift Linear in pressure
Y = Y0P
TE0214
Line mixing
6/22/2010
Residuals largest at the wings of strong lines
Conditions for line mixing Lower state energy gap is less
than thermal energy Line separation is less than width
E1 - E2 < kT
1 - 2 < 1,2