Line Mixing in Atmospheric Ozone Corey Casto and Frank C. De Lucia The Ohio State University International Symposium on Molecular Spectroscopy 66 th Meeting — June 20–24, /21/20111TE12

Experiment Quasi-Optical Isolator Pulse Generator DAQ BWO HV Power  Characteristics  10.3 m cavity  ~6000 resonances in the GHz range  ν FSR = 14.5 MHz  Q ~ 7 x 10 6  3 second scan time  Ringdown  α = 1/c τ  τ ~ 5 μ s InSb Detector 6/21/20112TE12

Collisions and lineshape  Collisions broaden spectral lines  Pressure  collision rate  linewidth  Inelastic and elastic collisions both occur  Elastic collisions also couple lines by inducing collisional transitions 6/21/20113TE12

Collisions and lineshape  Radiative transitions allow E″ → E′  Collisional transitions allow E 1 ↔ E 2  Kinetic energy determines coupling strength: kT ≳ Δ E  At high pressures mixing can be observed 6/21/20114TE12

Modeling line mixing  Coupling of each pair of lines can be described by a parameter related to collisional transitions  For n lines, the number of parameters is ~ n 2  Perturbation theory can limit the number of parameters to a more operable number 6/21/20115TE12

Modeling line mixing  First order perturbation approximation  Net effect of coupling with all other lines  Near wings skewed  Peak shift 6/21/20116TE12

Modeling line mixing  Peak value  α VVW  1/ δ  α R1  Y/ δ  Mixing is more significant at higher pressures 6/21/20117TE12

Modeling line mixing  Problems  Parameters must be measured at high pressures  Overlap can cause parameter correlations  Systematic effects contribute to parameter error  Solutions  Theoretical constraints on parameters  Multi-pressure fitting 6/21/20118TE12

Multi-pressure fits  No mixing parameters  Good fit 6/21/20119TE12

Multi-pressure fits  No mixing parameters  Fairly good fit  Significant residual around strong lines 6/21/201110TE12

Multi-pressure fits  Mixing parameters  Improved fit  Some residual at 245 GHz 6/21/201111TE12

Multi-pressure fits  Mixing parameters  No significant change in fit 6/21/201112TE12

Multi-pressure fits  Isolated lines show little mixing  Denser region shows more mixing 6/21/201113TE12

Summary  At low pressures spectral lines are isolated  At higher pressures, mixing can be observed  To first order, the Rosenkranz approximation significantly improves our model of the ozone spectrum  Measured parameters are consistent with expectations at a range of atmospheric pressures 6/21/201114TE12