Dissociative Electron Attachment to HCN and HNC

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Dissociative Electron Attachment to HCN and HNC
S. T. Chourou and A. E. Orel
Dept. of Applied Science, University of
California, Davis
STChourou_at_ucdavis.edu
Work supported by NSF Grant PHY-05-55401 and US
Department of Energy, Office of Basic Energy
Science
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Why HCN?

• Presence in Interstellar media and comets plays
  a major role in initial synthesis of amino acids
  (D. M. Rank et al. Science 174, 1083 (1971).)
• Interest in CN lasers presence of HCN is
  essential for pumping and electron impact may be
  critical (C.R. Quick et al. Opt. Commum. 18, 268
  (1976).)
• Computational interest Small polyatomic system
  for which nuclear dynamics amenable to study is
  full dimensionality.

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Outline

• State of the art
• Computational Approach
• Target Description
• Resonant States
• Dissociation Dynamics and Cross Sections

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Previous Work

• HCN/HNC (X1?g) e- ? (HCN-)( 2?g ) ? H (2S )
  CN- (1?)

Experimental results DEA cross section peaks at
2.26 eV 2 and 2.5 eV 3
Previous theoretical work p-shape resonance at
2. 6 eV 1
1-D (Diatomic) Picture
NO correlation between resonant state and final
products
Problem treatment in full dimensionality
1 D. W. Jain et al. Phys. Rev. A 32, Vol. 32,
134 (1985) 2 P. D. Burrow (Private
Communication) 3 M. Inoue, J. Chim. Phys. 63,
1061 (1966)
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Problem Formulation
Time-dependant Schrodinger Equation for Nuclear
Motion
(HCN or HNC)
With Initial State
Complex Potential Energy Surface (PES)
Where nuclei expressed in Jacobi coordinates
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Ab Initio Methods

• Electron Structure Calculations MCSCF, CAS and
  MRCI techniques (basis set Triple Zeta plus
  Polarization (TZP) diffuse functions for anion)
• Electron Scattering Calculations based on the
  Complex Kohn Variational Method (currently in the
  static exchange approximation)
• Nuclear Dynamics Calculations wavepacket
  propagation using the Multiconfiguration
  Time-Dependant Hartree (MCTDH) approach
  (Heidelberg Package H.-D. Meyer et al.
  Chem.Phys.Lett. 165, 73 (1990))

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Target PES and Initial States
CN--H
H--CN Initial wave packet
H--CN
CN--H
H--CN
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Ab Initio Methods

• Electron Structure Calculations MCSCF, CAS and
  MRCI techniques (basis set Triple Zeta plus
  Polarization (TZP) diffuse functions for anion)
• Electron Scattering Calculations based on the
  Complex Kohn Variational Method (currently in the
  static exchange approximation)
• Nuclear Dynamics Calculations wavepacket
  propagation using the Multiconfiguration
  Time-Dependant Hartree (MCTDH) approach
  (Heidelberg Package H.-D. Meyer et al.
  Chem.Phys.Lett. 165, 73 (1990))

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Resonant States
Evolution of resonances with R Eigenphase sum as
a function of electron energy in A symmetry
2D Cut of the resonant HCN- surfaces 12A and
22A
Eres (12A ) 0.11 a.u.
Eres (22A ) 0.26 a.u.
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Ab Initio Methods

• Electron Structure Calculations MCSCF, CAS and
  MRCI techniques (basis set Triple Zeta plus
  Polarization (TZP) diffuse functions for anion)
• Electron Scattering Calculations based on the
  Complex Kohn Variational Method (currently in the
  static exchange approximation)
• Nuclear Dynamics Calculations wavepacket
  propagation using the Multiconfiguration
  Time-Dependant Hartree (MCTDH) approach
  (Heidelberg Package H.-D. Meyer et al.
  Chem.Phys.Lett. 165, 73 (1990))

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Nuclear Dynamics
Target initial state CN--H
Target initial state H--CN
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DEA Cross Section
Preliminary results
Target initial state H--CN
Target initial state CN--H
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Summary and Future Work

• The DEA process to HCN and HNC is inherently
  polyatomic.
• Qualitative similarities in dissociation dynamics
  and quantitative differences in DEA cross
  sections for the two isomers.

• Include polarization and correlation effects for
  a more accurate description of the resonant
  states and investigative correlations with higher
  resonances.
• Reduce wavepacket reflections at grid boundaries
  by more efficient absorbing potentials.
• Invite experimentalists to do more detailed
  measurements in order to validate theory.

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Complex Kohn Variational Method
Variational Functional for the T-Matrix
(scattering amplitude)
Trial wave function for the N1 electron system
target
continuum
exchange
Correlation and Polarization
Continuum functions are further expanded in
combined basis of Gaussians and continuum
functions