Gas-phase Electron Diffraction István 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 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

Molecular Intensities

Probability Density Distributions

Scheme of Least-Squares Refinement

C6H3F3 and C6H3Cl3: Probability Density Distributions

Jahn-Teller Effect Edward 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   Jahn-Teller Effect MnF3 D3h C2v C2v Hargittai, M. et al. J. Am. Chem. Soc. 1997, 119, 9042.

MnF3 electron diffraction Hargittai, M. et al. J. Am. Chem. Soc. 1997, 119, 9042.

HS-CH2-CH2-SH Conformational Analysis

Estimating Mole Ratios

REPRESENTATIONS OF AVERAGE STRUCTURES rg rα re Perpendicular vibrations yes no Temperature Isotope

Comparison with Other Techniques Microwave spectroscopy X-ray crystallography Quantum chemical calculations NMR spectroscopy Vibrational spectroscopy Mass spectrometry Qualitative models