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Expansion Discharge Source for Ion Beam Spectroscopy of Cold Molecular Ions

Expansion Discharge Source for Ion Beam Spectroscopy of Cold Molecular Ions . Michael Porambo , Jessica Pearson, Craig Riccardo, Benjamin J. McCall International Symposium on Molecular Spectroscopy, The Ohio State University June 20, 2013. Outline. Motivation Review of Ion Beam Instrument

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Expansion Discharge Source for Ion Beam Spectroscopy of Cold Molecular Ions

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  1. Expansion Discharge Source for Ion Beam Spectroscopy of Cold Molecular Ions Michael Porambo, Jessica Pearson, Craig Riccardo, Benjamin J. McCallInternational Symposium on Molecular Spectroscopy, The Ohio State UniversityJune 20, 2013

  2. Outline • Motivation • Review of Ion Beam Instrument • Ion Source Work • Summary

  3. Molecular Ions Interstellar Chemistry CH5+ C6H7+ H2CO+ Oka Ion Factory, http://fermi.uchicago.edu/research/ch5plus/ Fundamental Chemical Physics Atmospheric Reactions Resolved, high precision spectroscopy to study these fields http://www.navy.mil/view_single.asp?id=40674 Combustion Processes NASA Picture of the Day, Expedition 13 Crew, International Space Station, NASA

  4. Challenges • Low number density • Small fraction of ions compared to neutrals • High rotational temperature

  5. Ion Production Methods Hollow Cathode Discharge Cell Supersonic Expansion Discharge No discrimination between ions and neutral molecules Positive Column Velocity Modulation Low rotational temperature No ion-neutral discrimination Ion-neutral discrimination High rotational temperature

  6. Ion Production Methods Way to bring low rotational temperature and ion-neutral discrimination together? Ion Beam Spectroscopy - last attempted in 1980s–1990s1 - advances in technology open new opportunities - can obtain both ion-neutral discrimination and low rotational temperatures 1Coe et al. J. Chem. Phys.1989, 90, 3893.

  7. Sensitive, Cooled, Resolved Ion BEam Spectroscopy - SCRIBES Electrostatic Bender2 Overlap region Low ion density 106 cm-3 Make up for this with cavity-enhanced spectroscopy Source chamber TOF mass spectrometer 2Kreckel et al. Rev. Sci. Instrum.2010, 81, 063304.

  8. Sensitive, Cooled, Resolved Ion BEam Spectroscopy – SCRIBES

  9. Spectroscopic Detection Noise Immune Cavity Enhanced - Optical Heterodyne Molecular Spectroscopy Cavity enhancement for longer pathlength (× Finesse/π)

  10. Spectroscopic Detection EOM Noise Immune Cavity Enhanced - Optical Heterodyne Molecular Spectroscopy NICE-OHMS Signal Heterodyne/Frequency Modulation Detection for Lower Noise

  11. Spectroscopic Detection EOM Noise Immune Cavity Enhanced - Optical Heterodyne Molecular Spectroscopy Lock-In Amplifier Also velocity modulate the ion beam and demodulate at this signal. NICE-OHMS Signal

  12. Spectroscopic Detection EOM Lock-In Amplifier NICE-OHMS Signal Frequency calibrated with optical frequency comb Line centers to ~1 MHz!

  13. Accomplishments Operational mass spectrometer Comb calibrated hot ion beam spectra in near-infrared (N2+) From Mills et al. J. Chem. Phys. 2011, 135, 224201. Mid-infrared optical system finished and optimized on CH4 First broadly tunable NICE-OHMS spectrometer in mid-IR From Porambo et al., Opt. Lett., 2012, 37, 4422.

  14. Next: Supersonic Expansion Discharge Source Produces ions with low rotational temperature Designed and characterized with H3+ cavity ring-down spectroscopy3 H3+ rotational temperature of 80–110 K3 Supersonic expansion discharge source in ion beam source chamber producing a nitrogenic expansion 3Crabtree et al., Rev. Sci. Instrum., 2010, 81, 086103.

  15. Ion source chamber moved to connect to Roots blower system Instrument Rearrangement Leybold RUTA 13000 system

  16. 10” bellows connected to Roots blower system Unistrut brace to prevent chamber from rising

  17. Source Chamber Beam skimmer used to extract ions from expansion

  18. Beam Skimmers Machined in-house from EDM graphite4 Two designs: 0.5 in. long, 3 mm diameter orifice5 1.024 in. long, 0.8 mm diameter orifice4 1 2 4Jordan et al., Rev. Sci. Instrum., 1999, 70, 1640. 5Keim, E. PhD Thesis, UC Berkeley, 1992.

  19. Preliminary Studies: Characterization of HN2+ Expansion Double-pass setup to perform wavelength-modulation optical heterodyne spectroscopy Rovibrational lines of HN2+ will be used to estimate a rotational temperature InSb Difference Frequency Generation

  20. Instrument Rearrangement Determine HN2+ rotational temperature by NICE-OHMS in ion beam Difference Frequency Generation setup

  21. Summary • Molecular ion spectroscopy is challenging but useful for studying many phenomena • Ion beam spectrometer development with ion-neutral discrimination, NICE-OHMS, and cold ions • Successful first signal and mid-infrared arrangement; now integrating source • Source works well in setup, attempting to finish characterization of rotational temperature • Preparing to extract ion beam from expansion

  22. McCall Research Group Former Members Brian Siller Andrew Mills ManoriPerera HolgerKreckel Kyle Crabtree Carrie Kauffman Acknowledgments Springborn Endowment NASA Earth and Space Science Fellowship Program

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