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1

Gas-phase actinide chemistry studies utilizing Fourier transform ion cyclotron resonance mass spectroscopy

John Langridge

Chem 5460

Dr. Chyan

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OutlineI. A generalized view of Mass Spectroscopy

II. Fundamentals of FTICR-MS

III. Why gas phase?

IV. Actinide studies – applicationWhy study Actinides?ReactivityKinetics and Reaction efficienciesThermodynamicsIonization 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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Fundamentals of FTICR-MSFunctions 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-MSIon 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 pr s on m/q w t outhigh eci i i h tr nsl t on la a i a n r / o us ne e g f c i g

• 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: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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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 radiusA. 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 studiesUniversity 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.

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Gas-phase ionizationLaser 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-MSStudied 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 signalA. 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 efficienciesEfficiency/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 reactionsHigher 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-MSBond 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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ConclusionsFirst 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

ReturnA. Marshall, et al., Mass Spectrometry Reviews 17 (1998), 1.

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