192
7 Molecular Structures from Gas-Phase Electron Diffraction
Fig. 7.10 Anharmonic
potential energy function
E(ρ) for 1,4-dioxin (ρ is the
large-amplitude
ring-puckering
coordinate). (Kochikov et al.
2002). Reproduced from
Journal of Molecular
Structure, 607. Kochikov IV,
Tarasov YI, Vogt N,
Spiridonov VP.
Large-amplitude motion in
1,4-cyclohexadiene and
1,4-dioxin: theoretical
background for joint
treatment of spectroscopic,
electron diffraction and
ab initio data, 163–174.
Copyright 2002, with
permission from Elsevier
Fig. 7.11 Molecular electron scattering intensities sM(s) calculated for the dynamic (line
with horizontal strokes) and static (solid line) anharmonic models of 1,4-cyclohexadiene (s in
Å −1 ). (Kochikov et al. 2002). Reproduced from Journal of Molecular Structure, 607. Kochikov IV,
Tarasov YI, Vogt N, Spiridonov VP. Large-amplitude motion in 1,4-cyclohexadiene and 1,4-dioxin:
theoretical background for joint treatment of spectroscopic, electron diffraction and ab initio data,
163–174. Copyright 2002, with permission from Elsevier
etc., are not possible without supporting data. In these cases, small differences
between values of related geometrical parameters and/or the values of some
parameters themselves are usually assumed or constrained according to results of
computations.
Equilibrium structure can be determined from electron diffraction data alone only
for simplest molecules and only when the quality of intensity measurements is good
enough (see, for instance, Hargittai et al. 1991; Vogt et al. 1995; Vogt 2001). For