Using Time of Flight Mass Spectrometry to Determine Temperature

1. Using Time of Flight Mass Spectrometry to Determine Temperature James C. Gleeson gleesonjc@appstate.edu James Cowart, Anthony Calamai, Adrian Daw Ion Trapping Group Department of Physics and Astronomy Appalachian State University Boone, NC

2. Ion Trap Experiments at AppState: Collision Rate Measurements of Hydrogen (ion collection) • currently investigating the reactions • First star formation, sunspots, ionospheric & interstellar chemistry Collision, Decay & Production Rates of Nitrogen (ion and photon collection) • Rate coefficients for N2++ and N2 • The dissociation rate of the molecular dication N2++ • The radiative lifetime of the 5S metastable level of N+ • Rate coefficient for N+(5S) quenching by • Cross Section for production of N+(5S) by dissociative electron impact ionization of N2

3. In general, rate coefficients depend on temperature… Strong temperature dependence (endothermic) Weak temperature dependence (Langevin-like rate)

4. Sample Time of Flight Spectra of H+, H2+, and H3+ with schematic of one of our ion traps…

5. Other experiments measuring ion cloud temperature… • Early work suggests that the average energy of ions stored in a harmonic rf quadrupole trap is 10% of the well depth (16 eV for this work) • Ifflander and Werth (1977) measured the line width of Ba+ 493 nm • Knight and Prior (1978) measured spatial distribution of metastable Li+ by laser scanning • Other work involves phase-stopped ejection • Champeau, et al. (1993) suggested temperature independent of well depth • Rocher, et al. (1998) • Fluorescence usually requires “special circumstances,” while phase-stopped ejection only gives a “snapshot” at 0o

6. The Basic Simulation • A SimIon 2-dimensional cylindrically symmetrical model of the entire apparatus • The simulation includes a storage period followed by a dump and detection period

7. Dump Voltages Time of Flight Spectra

8. Simulations for a “(7 x 3) mm” [(z x r) starting position] cloud(loosely speaking, z sets axial energy and r sets radial energy)

9. 3-D SimIon model with 0.3 mm size grid units using Cartesian geometry

10. Various potentials across the end caps Homemade (and soon to be replaced) pulsing circuit generates small potential difference (0.6 V) between trap end caps

11. “2x2 cloud” “4x2 cloud”

12. The Big Finish…

15. Future Work • Use this technique to estimate ion cloud “temperature” and uncertainty under different storage conditions (minimize χ2) • Photon imaging of the cloud as an alternative form of temperature measurement for comparison

16. Acknowledgements • Our work is funded by: • Research Corporation Award CC6409 • NSF Grant No. AST-04-06706 • Appalachian State University

18. Later studies may compare photon imaging of the cloud to estimate temperature For ground state reactants and products, the reaction: N2+N2++N2++N2+ has E = 11.5 eV.

19. Geom vs. Cyl