Chapter 7
Molecular Structures from Gas-Phase
Electron Diffraction
Abstract The determination of thermal-average and equilibrium molecular structures by conventional electron diffraction is reviewed. The history and theoretical basis of the method as well as the electron diffraction experiment are briefly
described. The significance of different structure types is explained. A particular
emphasis is put on the determination of semiexperimental equilibrium structure from
electron diffraction data taking into account vibrational corrections calculated with
quantum-chemical force fields.
7.1 Introduction
Gas-phase electron diffraction is a very important source of structure data for both
stable and unstable free molecules, both stable and unstable free radicals as well
as ions. Unlike microwave spectroscopy, this method is also applicable to study
the structure of nonpolar and relatively large molecules [see, for instance, the
porphyrazine derivative with 137 atoms (Zhabanov et al. 2015)]. Moreover, the
absence of isotopic species is not a problem for this method.
As can be revealed by means of the MOGADOC database (Vogt et al. 2003);
see Chap. 10 for more detail and monograph “Structure Data of Free Polyatomic
Molecules” (Vogt and Vogt 2019), about a half of all structure determinations
have been carried out by electron diffraction. About the same number of structure
studies has been performed by high-resolution spectroscopy methods all together
(see Fig. 7.1). Although the number of structure investigations has decreased in the
last decades, the structure determinations themselves have become more extensive.
In this chapter, before moving on to the main topic, the history, the gas-phase
electron diffraction experiment, and the theoretical basis of the method will be briefly
presented.
© Springer Nature Switzerland AG 2020
J. Demaison and N. Vogt, Accurate Structure Determination of Free
Molecules, Lecture Notes in Chemistry 105,
https://doi.org/10.1007/978-3-030-60492-9_7
167
Molecular Structures from Gas-Phase
Electron Diffraction
Abstract The determination of thermal-average and equilibrium molecular structures by conventional electron diffraction is reviewed. The history and theoretical basis of the method as well as the electron diffraction experiment are briefly
described. The significance of different structure types is explained. A particular
emphasis is put on the determination of semiexperimental equilibrium structure from
electron diffraction data taking into account vibrational corrections calculated with
quantum-chemical force fields.
7.1 Introduction
Gas-phase electron diffraction is a very important source of structure data for both
stable and unstable free molecules, both stable and unstable free radicals as well
as ions. Unlike microwave spectroscopy, this method is also applicable to study
the structure of nonpolar and relatively large molecules [see, for instance, the
porphyrazine derivative with 137 atoms (Zhabanov et al. 2015)]. Moreover, the
absence of isotopic species is not a problem for this method.
As can be revealed by means of the MOGADOC database (Vogt et al. 2003);
see Chap. 10 for more detail and monograph “Structure Data of Free Polyatomic
Molecules” (Vogt and Vogt 2019), about a half of all structure determinations
have been carried out by electron diffraction. About the same number of structure
studies has been performed by high-resolution spectroscopy methods all together
(see Fig. 7.1). Although the number of structure investigations has decreased in the
last decades, the structure determinations themselves have become more extensive.
In this chapter, before moving on to the main topic, the history, the gas-phase
electron diffraction experiment, and the theoretical basis of the method will be briefly
presented.
© Springer Nature Switzerland AG 2020
J. Demaison and N. Vogt, Accurate Structure Determination of Free
Molecules, Lecture Notes in Chemistry 105,
https://doi.org/10.1007/978-3-030-60492-9_7
167