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