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The Performance Of A Continuous Supersonic Expansion Discharge Source

The Performance Of A Continuous Supersonic Expansion Discharge Source. Carrie A. Kauffman , Kyle N. Crabtree, Benjamin J. McCall Department of Chemistry, University of Illinois June 24th, 2010. Outline. 1. Motivation. 2. Source Design. 3. Results. 4. Conclusion. Motivation. Motivation.

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The Performance Of A Continuous Supersonic Expansion Discharge Source

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  1. The Performance Of A Continuous Supersonic Expansion Discharge Source Carrie A. Kauffman, Kyle N. Crabtree, Benjamin J. McCall Department of Chemistry, University of Illinois June 24th, 2010

  2. Outline 1. Motivation 2. Source Design 3. Results 4. Conclusion

  3. Motivation

  4. Motivation • Interstellar medium: • Diffuse Molecular Clouds • Temp ~60 K • Density ~101–103 cm-3 • Dense Molecular Clouds • Temp ~20 K • Density ~104–106 cm-3

  5. Sensitive Cooled Resolved Ion BEamSpectroscopy For more on SCRIBES, please stay for RE06.

  6. Production of Cold Molecular Ions Trot~ 300+ K Trot~ 110-180 K

  7. Production of Cold Molecular Ions Trot ~ 110+ K -No spectral intensity dilution, reduced spectral congestion -> easy spectral assignment -Astrophyiscally relevant temperatures-> molecular fingerprint for astronomers

  8. Continuous Supersonic Expansion Discharge Source Small Orifice Trot≈ 5-30 K High Pressure Gas Low Pressure

  9. Continuous Supersonic Expansion Discharge Source Leybold 3-Stage Pumping System Pumping speed ~ 3600 L/s

  10. Basic Design Gas Input High Temp Silicone O-rings Cathode Macor Cap Anode Macor Spacer

  11. H3+ R(1,0) R(1,1)u R(2,2)l Rotational Constant: 43.56 cm-3 McCall, B.J. Ph.D. Thesis, University of Chicago, 2001.

  12. Experimental Set-up

  13. Source Conditions • 2-3 bar of backing pressure • Orifice Size: flared like a trumpet 0.5 to 4.1 mm in diameter • Typical Chamber Pressure 200-300 mTorr • Negative voltage applied to cathode and anode held at ground • Current: 10-130 mA

  14. Sample Spectra

  15. Results Low Current Regime • ↑ column density with increasing discharge current. • ↑ in rotational temperature with increasing discharge current. • Operated for over 150 hours without source failure.

  16. Results High Current Regime • ↑ column density • No change in rotational temperature • 50 hours of operation

  17. Comparison 1. Xu et al. Chem. Phys. Lett. 1995, 242 126-131. 2. Tom et al. J. Chem. Phys. 2010, 132, 081103. 3. Davis et al. Chem. Phys. Lett. 2001, 344, 23-30.

  18. Summary • Rotational temperatures in the range of 50-110 Kelvin. • Robust & durable design capable of operating for an extended period of time. • Ion densities comparable to pulsed sources Increased sensitivity! • Plans for improving this design will be tested by studying the ν1 fundamental band of HN2+.

  19. Acknowledgments For more information visit the McCall Research Group at http://bjm.scs.uiuc.edu

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