1. Cavity Ringdown Spectroscopy of Molecular Ions in a Fast Ion Beam Susanna L. Widicus Weaver, Andrew A. Mills, and Benjamin J. McCall Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign

2. The SCRIBES Instrument SCRIBES = Sensitive, Cooled, Resolved Ion BEam Spectroscopy Sensitive: IR cw cavity ringdown spectroscopy with minimum detectable absorption ~ 10 -9 cm -1 Cooled:cw supersonic expansion discharge source whichleads to adiabatic cooling of ions Resolved:high resolution with sub-Doppler linewidths Ion Beam:ion optics used to steer a collimated beam of ions into the drift region, where it can be probed by cw ringdown techniques

3. The SCRIBES Instrument

4. Outline cw-CRDS systems Ion sources Progress on SCRIBES development Upcoming SCRIBES projects

5. SCRIBES cw-CRDS Options 2 – 5  m Difference Frequency Generation (DFG) System Ti:Sapph 650 – 1000 nm pump laser dichroic mirror /2 /4 Nd:YAG 1064 nm AOM Glan laser prism PPLN High finesse cavity & drift region

6. SCRIBES cw-CRDS Options 920 – 985 nm External Cavity Diode Laser Laser AOM Mode-matching optics High finesse cavity & drift region Focusing optics and detector Wavemeter Herriott cell Etalon Finder

7. SCRIBES cw-CRDS Options 8.5  m Quantum Cascade Laser See talks RB08 & RD08 Cryostat with QCL Aspheric lens Mode-matching optics High finesse cavity & drift region Focusing optics & detector AOM Reference cell

8. SCRIBES Ion Sources DC Cold Cathode Source gas input V float V float + V dis ions + neutrals pyrex tube V float = 4 kV V dis = 3 kV I beam = 30  A

9. Sapphire insulating spacer V float V float + V dis SCRIBES Ion Sources Supersonic Ion Source 0.7 mm pinhole

10. Going Supersonic with SCRIBES Roots pump To Roots Pump (7500 cfm) To Turbo Pump (4800 cfm) source skimmer ion optics drift region ~10 -4 Torr ~10 -2 Torr

11. SCRIBES Progress ringdown cavity & drift region source chamber future home of the mass spec ion optics chamber

12. SCRIBES Progress 30  A from DC cold cathode discharge source Ion beam, ringdown cavity colinear Ion beam through ion optics, turned by quadrupole Ready to scan!

13. What not to do to your mirrors! quadrupole off quadrupole on quadrupole off e - and/or negative ions are hitting the RD mirror!

14. The Next Steps with SCRIBES … Development Deflector plate to divert negative ions & e - from mirror Supersonic source & skimmer Second quadrupole Mass spec Spectroscopy N 2 + : A 2  u -X 2  g + @ 950 nm H 3 + : 2 ← 0 @ 3.67  m other ions …

15. Planned SCRIBES Spectroscopy CH 3 OH 2 + Important to gas phase interstellar chemistry; internal rotation & inversion see TI09 & TI10 C 6 H 7 + Precursor to interstellar C 6 H 6 ; proton “walks” around ring CH 5 + Precursor to interstellar CH 4, other hydrocarbons; highly fluxional molecule C 3 H 3 + Precursor to interstellar c-C 3 H 2 ; simplest Hückel aromatic 4n+2

16. NSF CHE AFOSR UIUC NASA Laboratory Astrophysics The McCall Group http://astrochemistry.uiuc.edu Packard ACS Dreyfus Acknowledgements