Progress In The Development Of An Infrared Ion Beam Spectrometer

Outline Why molecular ion beam First generation SCRIBES instrument Improvements Development of the second generation SCRIBES Prospects Sensitive Cold Resolved Ion BEam Spectrometer

Why Use Molecular Ion Beam? Why molecular ions Astrochemistry Combustion Carbocation chemistry Fundamental insterest Δω depends on √1/Ufloat voltage Why fast ion beam Kinematic compression High resolution spectroscopy Fingerprint for molecular ions Andrew Mills, WH02 at 2:05pm

First Generation SCRIBES Instrument Modular Electron Multiplier Low ion beam current Overlap of the laser Anode Development of TOF-MS Cathode Iris Pulser Plate Ion Optics Ringdown Mirrors InSb Ion Optics Drift Region Quadrupoles Modeled after Saykally’s instrument (Saykally et al. J. Chem. Phys. 1989, 90 (8), 3893-3894)

Second Generation SCRIBES Source Modular instrumentation High ion beam current Improved ion optics Differential pumping

Ion Sources Considerations for the test application High ion density Fast ion beam without a big energy spread Low maintenance Supersonic source Cold cathode discharge source Rotationally cold ions Continuous source Modular Precursor gas Anode Cathode Fused Silica

Uncooled Cold Cathode Source with N2 Plasma 3.5 kV Anode 7.5 kV Extraction plate Ground N2 plasma ISource = 30 µA IBeam = 10 µA IOverlap = 1.5 µA

Ion Optics Einzel Lens Side view Frontal view

Cavity Region V- V+ Neutrals Laser path Ions only 3 mm 3 mm

Quadrupoles Output Input +V -V Collimated beam +V -V Diverging beam

Asymmetrical Deflector Plates Output parallel beam Input focused beam (+)V (-)V

Mass Selecting Region Identity of the masses Beam energy Beam energy spread Characterization method TOF mass spectrometer The new instrument is modular therefore working with different setup have become quite easy. We have moved to a CF system instead of chambers. We are able to profile the ion beams character on horizontal and vertical axis using BPMs, Apertures helps in overlapping the laser beam with the ion beam with better precision that prior instrument and also these apertures defines a highly collimated beam. Our mass spectrometer is also to easy to separate from the instrument. We also have faraday cups located at several positions to measure beam current as well as to trouble shoot any problems. We were lacking higher ion beam current from the source. We decided to keep the source from first generation SCRIBE instrument due to its simplicity. However we instrooduced better ion optics and differential pumping to improve the ion current. In the old instrument the cavity region was defined by the use of quadrupoles. Main problem with these was the fact we were unable to create a collimate ion beam and the overlap of the laser was ambiguous. Current setup has a bender to divert the ion beam off the source pathway, this works better than the quadrupole in creating a collimated beam. These small spertures help in alingment of the laser to the ion beam. First generation SCRIBE never made it to the mass spectrometer development, we full filled that dream in the second generation instrument to characterize the beam. Time-of-Flight Mass Spectrometer

Laser Collision Cell CO2 gas at 30 mTorr Ringdown mirror

Mass Spectrometer

Mass Spectrum of N2 Plasma Ion beam energy = 3580 V ± 10 V Power supply output = 3574 V

Ion modulated cavity ringdown spectroscopy Growth of SCRIBES Velocity modulated cavity enhanced spectroscopy cw-Cavity ringdown spectroscopy Supersonic source H3+ band (fundamental) Ion modulated cavity ringdown spectroscopy 2st Generation SCRIBES 1st Generation SCRIBES Test N2+ Meinel lines DFG laser

Acknowledgement McCall Group Funding

Questions?