Transcript Gas-phase actinide chemistry studies utilizing Fourier

Gas-phase actinide
chemistry studies utilizing
Fourier transform ion
cyclotron resonance mass
spectroscopy
John Langridge
Chem 5460
Dr. Chyan
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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
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I. A generalized view of Mass
Spectroscopy
How stuff works website; http://science.howstuffworks.com/mass-spectrometry3.htm
(accessed April 23, 2011)
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II. Fundamentals of FTICR-MS
Mayo clinic; http://www.mayomedicallaboratories.com/articles/hottopics/transcripts/2009/2009-3bhumangenome/3b-40.html ( accessed April 23, 2011)
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Fundamentals of FTICR-MS
Functions of ion mass
Radius
Velocity
Energy
Ion cyclotron frequency
A. Marshall, et al., Mass Spectrometry Reviews 17 (1998), 1.
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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 Reviews 17 (1998), 1.
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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)
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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 Reviews 17 (1998), 1.
J. K. Gibson, J. Marçalo, Coord. Chem. Rev. 250 (2006), 776.
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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 Reviews 17 (1998), 1.
J. K. Gibson, J. Marçalo, Coord. Chem. Rev. 250 (2006), 776.
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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 Reviews 17 (1998), 1.
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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 Reviews 17 (1998), 1.
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Cyclotron motion, excitation and
detection
University of Bristol: Center for mass spectroscopy http://www.chm.bris.ac.uk/ms/theory/fticrmassspec.html (accessed April 18, 2011)
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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 Reviews 17 (1998), 1.
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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 Reviews 17 (1998), 1.
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ICR orbital frequency vs. m/z
A. Marshall, et al., Mass Spectrometry Reviews 17 (1998), 1.
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ICR orbital radius vs. m/z
A. Marshall, et al., Mass Spectrometry Reviews 17 (1998), 1.
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III. Why gas-phase?
Simply put:
Avoids effect of lattice structure
J. K. Gibson, J. Marçalo, Coord. Chem. Rev. 250 (2006), 776.
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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)
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J. K. Gibson, et al, Eur. Phys. J. D. 45 (2007), 133.
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 Reviews 17 (1998), 1.
J. K. Gibson, J. Marçalo, Coord. Chem. Rev. 250 (2006), 776.
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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 Reviews 17 (1998), 1.
J. K. Gibson, J. Marçalo, Coord. Chem. Rev. 250 (2006), 776.
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IV. Why study actinides?
Better understanding of natural laws
Materials science applications
Waste management/weapons programs
Medical applications
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Application to actinide chemistry
Reactivity
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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 Reviews 17 (1998), 1.
J. K. Gibson, J. Marçalo, Coord. Chem. Rev. 250 (2006), 776.
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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.
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Reactivity of An+
Promotion energy driven, 5fn-26d7s (filled)
vs. 5fn-26d2 (open)
J. K. Gibson, J. Marçalo, Coord. Chem. Rev. 250 (2006), 776.
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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.
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Application to actinide chemistry
Kinetics and reaction efficiencies
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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 Reviews 17 (1998), 1.
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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.
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Reaction kinetics and efficiencies
Strong correlation: reaction efficiency 
promotion energy of An+
J. K. Gibson, J. Marçalo, Coord. Chem. Rev. 250 (2006), 776.
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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.
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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.
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Application to actinide chemistry
Thermodynamics
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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 Reviews 17 (1998), 1.
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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.
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Thermodynamics of actinide oxides
OPu+-O 250 kJ/mol too low
J. K. Gibson, J. Marçalo, Coord. Chem. Rev. 250 (2006), 776.
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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.
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Application to actinide chemistry
Ionization Energy and Bond Energy
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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 Spectrometry 228 (2003), 457.
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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.
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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
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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
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Cyclotron motion
Return
A. Marshall, et al., Mass Spectrometry Reviews 17 (1998), 1.
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