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Istv á n Hargittai Budapest University of Technology and Economics and Hungarian Academy of Sciences Gas-phase Electron Diffraction INTERNATIONAL SCHOOL OF CRYSTALLOGRAPHY 36thCourse: ELECTRON CRYSTALLOGRAPHY: NOVEL APPROACHES FOR STRUCTURE DETERMINATION OF NANOSIZED MATERIALS - PowerPoint PPT Presentation
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István HargittaiBudapest University of Technology and Economics
and Hungarian Academy of Sciences
Gas-phase Electron Diffraction
INTERNATIONAL SCHOOL OF CRYSTALLOGRAPHY
36thCourse: ELECTRON CRYSTALLOGRAPHY: NOVEL APPROACHES FOR
STRUCTURE DETERMINATION OF NANOSIZED MATERIALS
ERICE, SICILY: JUNE 9-20, 2004
Two-Volume Treatise on Gas-Phase Electron Diffraction
CO2 Curves from Gas-Phase Electron Diffraction
Brief History I
• 1912-15 X-ray crystallography, Laue, the Braggs, Debye
• 1924 de Broglie (wave nature of moving electrons)
• 1927 Davisson & Germer, G.P. Thomson solid-phase electron diffraction
• 1930 Mark and Wierl, first GED experiment• 1932 James, molecular vibrations• 1935 Pauling & Brockway, f(r)
Brief History II
• 1937-39-49 Finbak, Debye, Karle and Karle rotating sector-microphotometer method
• 1950s modern experimental apparatus• 1955 Bartell the physical meaning of geometrical
parameters• Last decades combined and concerted
application of various techniques• Fine effects (relativistic, Jahn-Teller, etc.)• Increasingly, quantum chemical calculations
Gas-phase electron diffraction experiment
Combined gas-phase electron diffraction/mass-spectrometric
experiment
Total Intensity Distribution and “Background”
Molecular Intensities
e
am
ji
N
i
N
j sr
srsslsg
R
IKsI
222
21
1 1ij2
02
m
sin)exp()()(
Molecular Intensities
Probability Density Distributions
Scheme of Least-Squares Refinement
C6H3F3 and C6H3Cl3: Probability Density Distributions
Jahn-Teller EffectEdward Teller (1908-2003)
“A nonlinear, symmetric molecule with an orbitally degenerate electronic state is unstable and gets distorted, thereby removing the electronic degeneracy, until a nondegenerate ground state is achieved.”
Jahn, H.A.; Teller, E. Proc. R. Soc. London A 1937, 161, 220.
Jahn-Teller Effect MnF3
D3h
C2v C2v
Hargittai, M. et al. J. Am. Chem. Soc. 1997, 119, 9042.
s
F
FF
Mn
MnF3 electron diffraction
Hargittai, M. et al. J. Am. Chem. Soc. 1997, 119, 9042.
0 1 2 3 4 5 6 7
E
TD 3h
Mn-F F∙∙∙F
f(r)
r, Å 0 1 2 3 4 5 6 7
E
T
Mn-F Mn-F F∙∙∙F F∙∙∙F
C 2v
f(r)
r, Å
HS-CH2-CH2-SH Conformational Analysis
Estimating Mole Ratios
RT
E
f
fn
N
N Δexp
2
1
2
1
rg rα re
Perpendicular vibrations yes no no no
Temperature yes yes no no
Isotope yes yes yes no
REPRESENTATIONS OF AVERAGE STRUCTURES
0αr
Comparison with Other Techniques
• Microwave spectroscopy• X-ray crystallography• Quantum chemical calculations• NMR spectroscopy• Vibrational spectroscopy• Mass spectrometry• Qualitative models