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
4. Conclusion
3. Results

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 BEam Spectroscopy
For more on SCRIBES, please stay for RE06.

6. Production of Cold Molecular Ions
Trot ~ 300+ K
Trot ~ 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+ Rotational Constant: 43.56 cm-3 R(1,0) R(1,1)u R(2,2)l
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 mTorr
Negative voltage applied to cathode and anode held at ground
Current: 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 This Work Xu et al.1 Tom et al.2 Davis et al.3
Type of Source
Continuous nozzle
Continuous slit-jet corona
Pulse Nozzle
Pulsed Slit
Rotational Temperature (K)
50-110 77
60-100
Not Reported
Ion Density (cm-3)
8 × 1010 to 2 × 1012
1 x 1011
5x1010
1. Xu et al. Chem. Phys. Lett. 1995,
2. Tom et al. J. Chem. Phys. 2010, 132,
3. Davis et al. Chem. Phys. Lett. 2001, 344,

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