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John Langridge Chem 5460 Dr. Chyan

Gas-phase actinide chemistry studies utilizing Fourier transform ion cyclotron resonance mass spectroscopy. John Langridge Chem 5460 Dr. Chyan. Outline. I. A generalized view of Mass Spectroscopy II. Fundamentals of FTICR-MS III. Why gas phase? IV. Actinide studies – application

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John Langridge Chem 5460 Dr. Chyan

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  1. Gas-phase actinide chemistry studies utilizing Fourier transform ion cyclotron resonance mass spectroscopy John Langridge Chem 5460 Dr. Chyan

  2. Outline • I. A generalized view of Mass Spectroscopy • II. Fundamentals of FTICR-MS • III. Why gas phase? • IV. Actinide studies – application • Why study Actinides? • Reactivity • Kinetics and Reaction efficiencies • Thermodynamics • Ionization and bond energy

  3. I. A generalized view of Mass Spectroscopy How stuff works website; http://science.howstuffworks.com/mass-spectrometry3.htm (accessed April 23, 2011)

  4. II. Fundamentals of FTICR-MS Mayo clinic; http://www.mayomedicallaboratories.com/articles/hottopics/transcripts/2009/2009-3b-humangenome/3b-40.html ( accessed April 23, 2011)

  5. Fundamentals of FTICR-MS • Functions of ion mass • Radius • Velocity • Energy • Ion cyclotron frequency A. Marshall, et al., Mass Spectrometry Reviews17 (1998), 1.

  6. Fundamentals of FTICR-MS • Ion cyclotron resonance (ICR) • ICR frequency = fundamental resonant frequency of species • Feature: Ions of given m/z are same regardless of velocity • When ICR = excitation frequency, cyclotron motion results • Cyclotron motion  high precision m/q without translational energy focusing • Factor separating FTICR-MS from other methods A. Marshall, et al., Mass Spectrometry Reviews17 (1998), 1.

  7. Fundamentals of FTICR-MS University of Bristol: Center for mass spectroscopy http://www.chm.bris.ac.uk/ms/theory/fticr-massspec.html (accessed April 18, 2011)

  8. Fundamentals of FTICR-MS:Components • Ion sources • External is best • Avoids magnetic perturbations • Sometimes at cost of ion optics A. Marshall, et al., Mass Spectrometry Reviews17 (1998), 1. J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  9. Fundamentals of FTICR-MS:Components • Ion trapping  E field + H field • Trapping alone  kinetic energy + mass/charge • ICR frequency sweep  orbital transition • Collision induced dissociations (CID) of ions with gas • Changing system A. Marshall, et al., Mass Spectrometry Reviews17 (1998), 1. J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  10. Fundamentals of FTICR-MS:Components • Detection: ion  time varying AC signal • Current  AC “image” coupling to detector plates • analogous to broadcast model • Ions are part of the circuit! A. Marshall, et al., Mass Spectrometry Reviews17 (1998), 1.

  11. Fundamentals of FTICR-MS:Components • Fourier transformation • Time domain  frequency domain • ICR frequency proportional to m/z • Increases potential resolution • Ion is “seen” multiple times – high path length • Averaging: improved S/N A. Marshall, et al., Mass Spectrometry Reviews17 (1998), 1.

  12. Cyclotron motion, excitation and detection University of Bristol: Center for mass spectroscopy http://www.chm.bris.ac.uk/ms/theory/fticr-massspec.html (accessed April 18, 2011)

  13. Useful application: excitation cyclotron motion • Not mutually exclusive • 3 common configurations • Acceleration to larger radius then detection • Increase KE above threshold for reaction or dissociation  CID • Mass selection as a function of acceleration and increased radius A. Marshall, et al., Mass Spectrometry Reviews17 (1998), 1.

  14. Uses for cyclotron excitation • ICR  higher potential mass resolution • Path length of excited ion is > 30000km/1s time scale • Few ions used (comparatively speaking) to minimize space charge perturbations A. Marshall, et al., Mass Spectrometry Reviews17 (1998), 1.

  15. ICR orbital frequency vs. m/z A. Marshall, et al., Mass Spectrometry Reviews17 (1998), 1.

  16. ICR orbital radius vs. m/z A. Marshall, et al., Mass Spectrometry Reviews17 (1998), 1.

  17. III. Why gas-phase? Simply put: Avoids effect of lattice structure J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  18. Classical view of gas-phase interactions (CID) • Attraction between ion and neutral • Potential well forms from attraction • Exceed the reaction barrier E  products • Supersonic expansion  kinetic studies University of Bristol: Center for mass spectroscopy http://www.chm.bris.ac.uk/ms/theory/fticr-massspec.html (accessed April 18, 2011) J. K. Gibson, et al, Eur. Phys. J. D. 45 (2007), 133.

  19. Gas-phase ionization • Laser ablation with prompt reaction and detection (LAPRD) • Laser ablates metal to vapor • Prompt reaction with neutral OR • Laser/metal ablation  plasma acceleration to trap • Backing gas introduces species to ion trap A. Marshall, et al. Mass Spectrometry Reviews17 (1998), 1. J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  20. Gas-phase ionization • Laser desorption ionization • An-Pt alloy, 2% weight • Singly and doubly charged cations • Direct coupling to trap  reduced loses A. Marshall, et al. Mass Spectrometry Reviews17 (1998), 1. J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  21. IV. Why study actinides? • Better understanding of natural laws • Materials science applications • Waste management/weapons programs • Medical applications

  22. Application to actinide chemistry Reactivity

  23. Reactivity and FTICR-MS • Studied via LAPRD and LDI • Neutral/ion interaction  quadrupole stage/ion trap. • Alkene interactions; electron density in double bond available upon activation • Fragmentation = mass change  bond formation provide clues about reactions • Relative abundance = amplitude of the frequency domain signal A. Marshall, et al. Mass Spectrometry Reviews17 (1998), 1. J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  24. Reactivity of actinide ions (1+) • Th+ > Pa+ > U+ = Np+ > Cm+ > Pu+ > Bk+ > Am+ = Cf+ > Es+ • Thorium  transition metal character • Curium  half filled f-orbital • Plutonium / Americium  no 6d J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  25. Reactivity of An+ • Promotion energy driven, 5fn-26d7s (filled) vs. 5fn-26d2 (open) J. K. Gibson, J. Marçalo, Coord. Chem. Rev. 250 (2006), 776.

  26. Actinyl ion vs. An2+ • ThO+, UO+ , UO22+ only slightly reactive • Strong metal ion to oxygen bond  impacts reactivity • Th 2+ and U2+ • Highly activating to hydrocarbons, particularly arenes • cationic charge abstraction (2+)  More efficient than 1+ J. Marcalo, J.P. Leal, A. P.de. Matos, Organometallics 16 (1997), 4581.

  27. Application to actinide chemistry Kinetics and reaction efficiencies

  28. Kinetics, reaction efficiencies and FTICR-MS • Change must accompany ion-neutral collisions (product formation) • Frequency domain studied in a time domain  “how does frequency change over a span of time?” • Concentrations related to relative amplitudes of signals A. Marshall, C. Hendrickson, G. Jackson, Mass Spectrometry Reviews17 (1998), 1.

  29. Reaction kinetics and efficiencies • Efficiencies  ratio of experimental data and theoretical calculations • Kexp / Kcol = reaction efficiency • Kcol  theoretical collisional rate constant J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  30. Reaction kinetics and efficiencies • Strong correlation: reaction efficiency  promotion energy of An+ J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  31. Reaction kinetics and efficiencies • Efficiency/promotion energy correlation does not strictly exist for An2+ species • Ground state  divalent state = high promotion energy with 2 unpaired non-f electrons for all but Th2+ J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  32. Promotion energy and kinetics • Promotion energy controls reactions • Higher promotion energy indicates kinetic restrictions M. Santos, et al. Int. J. Mass Spectrometry 228 (2003), 457.

  33. Application to actinide chemistry Thermodynamics

  34. Thermodynamics and FTICR-MS • Bond dissociation energy • Energy of known sample fragment based on resonant freq and Kinetic Energy • CID fragments sample further • Results in a new resonant frequency • Difference in E is BDE A. Marshall, C. Hendrickson, G. Jackson, Mass Spectrometry Reviews17 (1998), 1.

  35. Thermodynamics of actinide oxides • Oxidation studies  BDE • Broad range of Oxygen dissociation energies known • An+-O, An2+-O, OAn+-O, OAn2+-O J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  36. Thermodynamics of actinide oxides • OPu+-O 250 kJ/mol too low J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776.

  37. Thermodynamics of actinide oxides • Recently: PaO22+ intermediate state between 5+ and 6+ • Experimentally and computationally confirmed • Thermodynamic instability in the species • Similar to simultaneous multi-state behavior seen in plutonium (4 states in single solution) J. K. Gibson, et al. Eur. Phys. J. D. 45 (2007), 133.

  38. Application to actinide chemistry Ionization Energy and Bond Energy

  39. Ionization energy-actinide oxides • Ions reacted with neutrals of known IE (CID) • Electron transfer of ion  neutral • Establishes limits of ion electron affinities of the neutrals • 2+ difficult due to coulombic interactions in product  increase energy barriers • Formation enthalpy estimates made from bond and ionization energies J. K. Gibson, J. Marçalo, Coord. Chem. Rev.250 (2006), 776. J. K. Gibson, et al. Eur. Phys. J. D.45 (2007), 133. M. Santos, et al. Int. J. Mass Spectrometry228 (2003), 457.

  40. Complications of studying late actinides – issue one • Sample size • Sub-milligram (literally microgram) samples typical • Highly efficient ion source • Smaller sample = fewer ions; 10-100 trapped ions necessary for decent resolution J. K. Gibson, et al. Eur. Phys. J. D.45 (2007), 133.

  41. Complications of studying late actinides – issue two • Half-life • Late / Trans-actinides half-life < 1s • Isotope production facility directly coupled to trap J. K. Gibson, et al. Eur. Phys. J. D. 45 (2007), 133

  42. Conclusions • First time comparison of theoretical and experimental actinide data • FTICR-MS = High resolution  high path length • Combine with other MS techniques • High flexibility; many options • Via ion manipulations

  43. Cyclotron motion Return A. Marshall, et al., Mass Spectrometry Reviews17 (1998), 1.

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