Helium Nanodroplet Isolation HENDI:Electrom Impact Ionisation of Embedded Haloalkanes

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DEPARTMENT OF CHEMISTRY
Helium Nanodroplet Isolation (HENDI) Electron
Impact Ionisation of Embedded Haloalkanes Scott
M. Brereton, Shengfu Yang, Martyn D. Wheeler,
Andy M. Ellis
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What is a Helium Nanodroplet?

• Cluster of 100-100,000 He atoms
• Internal Temperature 0.37 K
• Exhibits Superfluidity
• Individual He binding energy 4 cm-1

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Helium Superfluidity

• Uniform Temperature
• Zero Viscosity (Shear Limited)
• Extremely High Thermal Conductivity
• Quiescent Boiling

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Why HENDI?

• Cold
• Inert
• Liquid

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Producing Helium Nanodroplets

• He is pre-cooled to 11 K
• He with a stagnation pressure of 20 bar is
  expanded through a pulsed valve (General Valve
  Series 99) into a diffusion pumped vacuum
  chamber.
• Pulsed Nanodroplet source
• 100,000 He atoms in droplet

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HENDI Experiment
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Multiple Toluene Pick-up
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HENDI-TOF

• Do Nanodroplets provide a soft ionisation
  environment?
• Evidence from SF6 in nanodroplet1
• Compare standard EI mass spectra with EI in
  nanodroplet

A. Scheidemann, B. Schilling and J. P. Toennies,
J. Phys. Chem. 1993, 97, 2128-2138
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Ionisation in Nanodroplets
Hen.X e-
Hen.X 2e-
He(n-2).He2.X
He(n-(2a)).He2.X aHe
He(n-a).X
He(n-(ab)).X bHe
He(n-(ab)) X
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CHCl3
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CHBr3
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Cl(CH2)3Cl
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ClCH2CHClCH3
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Conclusions (I)

• Sucessfully constructed a pulsed helium
  nanodroplet source
• Nanodroplet size of gt 10,000 He atoms (as
  evidenced by pick-up of multiple dopant
  molecules)

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Conclusions (II)

• Preliminary study of E.I. On haloalkane doped
  nanodroplets shows droplets not to be a soft
  ionisation source
• Moving forward Laser spectroscopy of molecules,
  and hopefully, free radicals in helium droplets

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Thanks / Acknowledgments

• Departmental Workshop Staff
• Keith Wilkinson
• John Weale
• Carl Schieferstein
• Gerry Butler
• Funding