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High-Precision Sub-Doppler Infrared Spectroscopy of HeH +

High-Precision Sub-Doppler Infrared Spectroscopy of HeH +. Adam J. Perry , James N. Hodges, Charles Markus, G. Stephen Kocheril , Paul A. Jenkins II, and Benjamin J. McCall 69 th International Symposium on Molecular Spectroscopy University of Illinois at Urbana-Champaign 20 June 2014 FA01.

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High-Precision Sub-Doppler Infrared Spectroscopy of HeH +

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  1. High-Precision Sub-Doppler Infrared Spectroscopy of HeH+ Adam J. Perry, James N. Hodges, Charles Markus, G. Stephen Kocheril, Paul A. Jenkins II, and Benjamin J. McCall 69th International Symposium on Molecular Spectroscopy University of Illinois at Urbana-Champaign 20 June 2014 FA01

  2. Overview • Introduction • Spectroscopic Technique • Results • Future Directions/Conclusions He H

  3. HeH+ Background • HeH+ is one of the first molecules formed in the early universe • Thought to be present in many astronomical environments • Planetary nebulea • Dense clouds • Supernovae • No unequivocal detection has been made Hubble Space Telescope image of the planetary nebulae NGC 7027. From http://apod.nasa.gov/apod/ap130826.html S. Lepp, Astrophys. SpaceSci. 285, 737 (2003) S. Lepp, P. C. Stancil, and A. Dalgarno, J. Phys. B 35, R57 (2002) Dabrowskiand G. Herzberg, Top. N. Y. Acad. Sci. 2 38, 14 (1977) J. H. Black, Astrophys. J. 222, 125 (1978) W. Roberge and A. Dalgarno, Astrophys. J. 255, 489 (1982)

  4. Theoretical Investigations • Simplest 2-electron system/heteronuclear molecule • Excellent benchmark for ab initio calculations with QED and relativistic corrections • Great for studying isotope effects • Breakdown of Born-Oppenheimer Approx. • See talk FA02 next • Along with H2 and H3+, only other molecule to have rovibrational transitions calculated with spectroscopic accuracy (~0.01 cm-1) K. Pachucki, and J. Komasa, J. Chem. Phys137, 204314 (2012) W. Tung, M. Pavanello, and L. Adamowicz, J. Chem. Phys. 137, 164305, (2012)

  5. Previous Experimental Work • First rovibrational spectrum in 1979 by Tolliver et al. • Doppler-tuned ion beam • P(12) and P(13) lines • P(4)-R(4) observed by Bernath and Amano (1982) • 30-60 MHz uncertainty • P(5)-P(6) and R(5)-R(7) measured by Crofton et al. (1989) • Rotational work by Liu, D. et al., Matsushima et al.,and Liu, Z. et al. Spectrum of R(1) transition recorded by Bernath and Amano (1982) • D. Tolliver, G. Kyrala, and W. Wing, Phys. Rev. Lett., 19, 1719-1722 (1979) • P. Bernath and T. Amano, Phys. Rev. Lett., 48, 20-22, (1982) • D. Liu, W. Ho, and T. Oka, J. Chem. Phys, 87, 2442, (1987) • M. Crofton, R. Altman, N. Haese, J. Chem. Phys., 91, 5882 (1989) • F. Matsushima, T. Oka, and K. Takagi, Phys. Rev. Lett. 78, 1664-1666 (1997) • Z. Liu, and P. Davies, Phys. Rev. Lett., 79, 2779-2782 (1997) • Z. Liu, and P. Davies, J. Chem. Phys, 107, 337 (1997)

  6. Spectroscopic Method Velocity Modulation (Ion-neutral discrimination) NICE-OHVMS Heterodyne Detection (Reduction of 1/f technical noise) Cavity Enhancement (Increase signal strength) Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS) B. M. Siller, et al. Opt. Express 19, 24822-7, (2011)

  7. NICE-OHVMS Spectrometer 40 kHz Frequency Comb Wave-meter to PZT PZT OPO 3.2-3.9 µm nidler= npump-nsignal ~3 MHz AOM EOM Lock-In Amplifier Lock-In Amplifier f = 80 kHz 80 MHz YDFL X & Y Channels X & Y Channels ν 90o Phase Shift Slow Fast Lock Box

  8. Comb Scanning Rep. rate tuned so that signal beat lies within bandpass filter on frequency counter Frequency correction applied by AOM keeps signal beat within the bandpass AOM Comb Modes Pump offset locked (~20 MHz) to nearest comb mode Frequency Bandpass regions (on frequency counter)

  9. HeH+ Production • Plasma Conditions: • 1.8 Torr He • 10 mTorr H2 • 40 kHz , 170 mA discharge • Liquid N2 cooled • Signal very sensitive to H2:He ratio HeH+ + H2 → He + H3+

  10. Sample NICE-OHVMS Spectrum of HeH+ • P(1) Fundamental band transition • S/N ~ 140-275 • Doppler Width ~800 MHz

  11. Lamb Dip Fit Linecenter: Previous: 85258146.91(35) MHz 85258082(60) MHz

  12. Measured Transition Frequencies • P. Bernath and T. Amano, Phys. Rev. Lett., 48, 20-22, (1982)

  13. Spectroscopic Constants a. Fixed at value of Matsushima et al. b. Fixed to ab initio values • F. Matsushima, T. Oka, and K. Takagi, Phys. Rev. Lett. 78, 1664-1666 (1997) • Z. Liu, and P. Davies, J. Chem. Phys, 107, 337 (1997)

  14. Conclusions • HeH+ studied with NICE-OHVMS • Measured 4 fundamental band transitions of HeH+ with precision of ~1 MHz • Improved precision on the band origin and B1 • These new measurements plus ones currently underway should aid theorists calculating empirical potentials • (see talk FA02 next)

  15. Acknowledgments • Advisor: Ben McCall • Group Members: • James Hodges • Charles Markus • George Kocheril • Paul Jenkins • Funding Agencies

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