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

TE025

High Pressure

6/22/2010

Similar noise to low pressure

Discrepancies near line peaks

Causes?

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

TE0215

Future Work

6/22/2010

Model line mixing Which lines mix?

What are reasonable parameters?

Explore other dense spectra Formaldehyde (H2CO)

Nitric acid (HNO3)

Nitrogen dioxide (NO2)

Acetonitrile (CH3CN)

Methanol (CH3OH)