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Initial Development of High Precision, High Resolution Ion Beam Spectrometer in the Near-Infrared

Initial Development of High Precision, High Resolution Ion Beam Spectrometer in the Near-Infrared. Michael Porambo , Brian Siller, Andrew Mills, Manori Perera, Holger Kreckel, Benjamin J. McCall International Symposium on Molecular Spectroscopy The Ohio State University 18 June 2012.

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Initial Development of High Precision, High Resolution Ion Beam Spectrometer in the Near-Infrared

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  1. Initial Development of High Precision, High Resolution Ion Beam Spectrometer in the Near-Infrared Michael Porambo, Brian Siller, Andrew Mills, Manori Perera, Holger Kreckel, Benjamin J. McCall International Symposium on Molecular Spectroscopy The Ohio State University 18 June 2012

  2. Outline • Introduction: Why a Fast Ion Beam? • Ion Beam Description • NIR Spectra • Summary and Future Work

  3. Molecular Ions Important in many areas of nature and science Atmospheric science Astrochemistry NASA Picture of the Day, Expedition 13 Crew, International Space Station, NASA Fundamental physics and chemistry Challenge: How to produce ions in the laboratory effectively to study them? CH5+ From B. J. McCall, Ph.D. Thesis, Univ. of Chicago, 2001. From White et al. Science, 1999, 284, 135–137. C3H2 C3H C3H3+ e e H2 C3H+ C+ C2H2 C2H e C2H4 C2H3+ e C2H5+ e C+ CH4 CH3+ e CH3OCH3 CH5+ C2H5CN CH3OH, e CH3CN, e CH3OH H2O, e H2 CH3CN HCN, e CH3+ CO, e NH3, e CH2CO CH3NH2 H2 e N, e CH2+ CH HCN H2O H2 H3O+ e CH+ OH H2O+ H2 C OH+ HCO+ H2 H3+ O CO H2 H2+

  4. Ion Production Methods Hollow Cathode No ion-neutral discrimination Way to bring low rotational temperature and ion-neutral discrimination together? Supersonic Expansion Low rotational temperature No ion-neutral discrimination Positive Column Ion-neutral discrimination with velocity modulation No low rotational temperature Ion Beam Spectroscopy -last attempted in 1980s–1990s1 -advances in technology open new opportunities 1Coe et al. J. Chem. Phys.1989, 90, 3893.

  5. Sensitive, Cooled, Resolved Ion BEam Spectroscopy – SCRIBES Electrostatic Bender2 Rigorous ion-neutral discrimination Can perform low temperature spectroscopy with a supersonic discharge source Low ion density Make up for this with cavity-enhanced spectroscopy Overlap region Source chamber Laser in cavity TOF mass spectrometer 2Kreckel et al. Rev. Sci. Instrum.2010, 81, 063304.

  6. Sensitive, Cooled, Resolved Ion BEamSpectroscopy – SCRIBES

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

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

  9. 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

  10. Doppler Splitting Ion Beam nblue nred Mass information encoded in the optical spectrum! Ion Beam

  11. First Spectroscopic Target • Obtain rovibronic spectral transitions of Meinel band of N2+ • Near-infrared transitions probed with commercial tunable titanium–sapphire laser (700–980 nm) • N2+ formed in cold cathode ion source; no rotational cooling

  12. Experimental N2+ Signal Absorption Fractional Absorption (× 10−7) Dispersion No absorption observed! Frequency (cm−1) • Absorption signal strongly attenuated by saturation.3 Not observable! • Saturation parameters: 30,000 carrier, 6300 sidebands. • Dispersion signal attenuated by a factor of 2 due to saturation. 3Ma et al. J. Opt. Soc. Am. B2008, 25, 1144–1155.

  13. Spectral Signals From Mills et al. J. Chem. Phys. 2011, 135, 224201. • Obtain line centers, linewidths, and amplitudes from fits • FWHM ≈ 120 MHz (at 4 kV)

  14. TOF MS From Mills et al. J. Chem. Phys.2011, 135, 224201. Mass spectrum of nitrogenic ion beam. Energy spread in inset corresponds to an expected linewidth of 120 MHz.

  15. Spectral Signals From Mills et al. J. Chem. Phys. 2011, 135, 224201. • Obtain line centers, linewidths, and amplitudes from fits • FWHM ≈ 120 MHz (at 4 kV) • Noise equivalent absorption ~ 2 × 10−11 cm−1 Hz−1/2 (50× lower than last ion beam instrument)1 • Within ~1.5 times the shot noise limit! 1Coe et al. J. Chem. Phys.1989, 90, 3893.

  16. Ultra-High Resolution Spectroscopy • Rough calibration with Bristol wavelength meter (~70 MHz precision) • Precisely calibrate with MenloSystems optical frequency comb (<1 MHz accuracy)

  17. Frequency Comb Calibrated Spectra Average the line centers Average the line centers Only ~8 MHz from line center obtained in N2+ positive column work.4 Confident in improvements in the mid-IR. 4Siller, B. M. et al. Opt. Express2011, 19, 24822.

  18. Summary and Conclusions • Ion Beam Spectroscopy – effective in studying molecular ions. • High sensitivity spectroscopy used to study ion beam – high S/N, Doppler splitting. • Spectroscopy on rovibronic transitions of N2+ – first direct spectroscopy of electronic transition in fast ion beam. • Accurate frequency calibration with optical frequency comb.

  19. Present and Future Work • Ro-vibrational spectroscopy in the mid-IR • Integration of supersonic cooling • Stay tuned to MG05 for more information!

  20. Acknowledgments McCall Research Group Machine Shop Electronics Shop Jim Coe Rich Saykally Sources of Funding • Air Force • NASA • Dreyfus • Packard • NSF • Sloan • Research Corp. • Springborn Endowment

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