1. Measurement and Analysis of Atmospherically Broadened Linewidths and Lineshapes in the Millimeter Spectral Region Corey Casto Frank C. De Lucia The Ohio State University International Symposium on Molecular Spectroscopy on Molecular Spectroscopy 64 th Meeting — June 22-26, 2009

2. Background Ringdown  = 1/c  RD Millimeter region = 172-262GHz Atmospherically broadened lines  ~ 100MHz-5GHz –van Vleck-Weisskopf line shape –Line overlap –Line mixing/coupling Ozone

3. Experiment Cavity characteristics – ~6000 resonances – 3s scan period – FSR = 14.5 MHz –  RD ~ 5  s – Q ~ 7x10 6 BWO Quasi-Optical Isolator Mylar® beam splitter Output Coupling Hole InSb Detector Vacuum Chamber DAQ Pulse Generator HV Power Supply 10.3 m

4. Cavity losses Sources of vacuum absorption: –Diffraction –Reflection –Coupling –Systematic nearly periodic losses

5. Sulfur dioxide Fit using catalog parameters P dry = 101.6 torr P SO 2 = 77.0 mtorr T = 295.6 K JPL line strengths HITRAN line broadening parameters ~10% error

6. Sulfur dioxide Fit using free width parameters P dry = 101.6 torr P SO 2 = 76.2 mtorr T = 295.6 K JPL line strengths Least squares fit broadening parameters ~3% error

7. Sulfur dioxide Comparing parameters Fit values ~10% Lines with large overlap give unreliable widths

8. Ozone Fit using free width parameters P dry = 100.6 torr P O 3 = 160.8 mtorr T = 273.1 K JPL line strengths Least squares fit broadening parameters ~3% error

9. Ozone Fit using free width parameters P dry = 765.9 torr P ozone = 226.1 mtorr T = 263.5 K JPL line strengths Least squares fit broadening parameters ~6% error

10. Ozone Fit comparison Lower pressures agree with MLS width parameters Higher pressures tend toward bigger changes Greater overlap gives less physically meaningful width parameters

11. Future Reduce periodic losses Global fit Line mixing parameters

12. Thank You

13. Ozone Contaminants P dry = 117 torr P ozone = 262.2mtorr T = 293.6 K Formic acid Formaldehyde Water Other contaminants

14. Ozone Line Mixing? M.Yu. Tretyakov, G.Yu. Golubiatnikov, V.V. Parshin, M.A. Koshelev, S.E. Myasnikova, A.F. Krupnov, and P.W. Rosenkranz, J. Mol. Spectrosc. 223 (2004) 31-38.

15. Ozone Systematic effects Systematic cavity losses are not being subtracted out at higher absorption levels