1. High Precision Spectroscopy of CH 5 + with NICE-OHVMS James N. Hodges, Adam J. Perry and Benjamin J. McCall

2. Outline Motivation CH 5 + Experimental Challenges Current Data Future Direction

3. Infrared Spectroscopy of CH 5 + First Observed in 1999 by White, Tang & Oka Observed by Velocity Modulation Spectroscopy To this day remains completely unassigned E.T. White, J. Tang & T. Oka. Science, 284, 135 (1999). Above: CH 5 + Right: Infrared Spectrum of CH 5 +.

4. Infrared Spectroscopy of CH 5 + 917 Lines Observed Assignment by Subtraction – Removed the spectrum of other species: H 3 +, CH 3 +, C 2 H 3 +, HCO +, HCNH +, CH 4 and Rydberg H 2 E.T. White, J. Tang & T. Oka. Science, 284, 135 (1999).

5. Potential Energy Surface The potential energy surface –120 mimina of C s (I) –120 C s (II) saddlepoints ~ 40 cm -1 above minimum –60 C 2v saddlepoints ~ 300 cm -1 above minimum E.T. White, J. Tang & T. Oka. Science, 284, 135 (1999). X. Wang & T. Carrington Jr. J. Chem. Phys., 129, 234102 (2008). C s (I) C s (II)C 2V

6. Potential Energy Surface E.T. White, J. Tang & T. Oka. Science, 284, 135 (1999). X. Wang & T. Carrington Jr. J. Chem. Phys., 129, 234102 (2008). Zero Point Energy 10917 cm -1 ~ 300 cm -1 ~ 40 cm -1

7. Instrumental Layout OPO YDFL EOM Lock-In Amplifier X & Y Signal Lock-In Amplifier X & Y Signal Wave- meter 40 kHz Plasma Frequency 80 MHz 1 × Cavity FSR 90 o Phase Shift IPSIPS 2f i  p  s Freq. Comb AOM K. N. Crabtree, et al. Chem. Phys. Lett. (2012), 551, 1-6.

8. Comb Calibration Wave- meter Freq. Comb AOM […] SignalPump

9. Comb Calibration Wave- meter Freq. Comb AOM […] SignalPump

10. Comb Calibration Wave- meter Freq. Comb AOM […] SignalPumpSignal

11. Production of CH 5 + Velocity modulated, l-N 2 cooled, positive column H 3 + + CH 4  CH 5 + + H 2 Low current: ~ 80 mA 6 kHz modulation frequency Ratio 50:1 H 2 :CH 4 Total pressure ~ 1 Torr E.T. White, J. Tang & T. Oka. Science, 284, 135 (1999).

12. Technical Challenges Lower modulation frequency  lower current Lower frequency  greater noise Higher frequencies  lower pressures

13. Technical Challenges No PlasmaHigh current (40 kHz)Low current (6 kHz)

14. Last Year’s Line Wavenumber (cm -1 ) S/N ~ 25

15. Experimental Comparison ParameterOkaUs Current (mA)80200 Frequency (kHz)640 Pressure (Torr)11 H 2 :CH 4 50:1 ~ 50:1

16. Mirror Absorbance

18. Improvements Baked Mirrors –Operating in dry purge box –Prevented rapid degradation of performance

19. Improvements Included a  -emitter – 63 Ni –Less plasma noise in lock –Attain lower current

20. Recent Work CH 5 + line @ 2898 cm -1. Approximately 0.5 Intensity as Oka’s line @ 2926 cm -1. S/N ~ 30

21. Experimental Comparison ParameterOkaUs Current (mA)80110 Frequency (kHz)646 Pressure (Torr)10.250 H 2 :CH 4 50:1 ~ 30:1

22. Calibrated Scans and Fits Linecenter (MHz) SNR  (MHz) Oka Uncertainty (MHz) Obs.- Oka (MHz) 86880179505 MHz90-18085 MHz

23. Calibrated Scans and Fits Linecenter (MHz) SNR  fit (MHz) Oka Uncertainty (MHz) Obs.- Oka (MHz) 8772025340 ~ 2 MHz90-180200 MHz

24. Future Outlook New Mirrors –Have specialized coating –Improved Performance  Lamb dips Complete 917 lines 4-line combination differences with complete data set.

25. Acknowledgements Springborn Fellowship NSF GRF (DGE 11- 44245 FLLW)