One of the ways to determine the geometrical structure of gaseous molecules is the gas electron diffraction method. In this method, highly accelerated electron beams are shot into molecules. After colliding with the target molecules, the electrons are scattered. Information on the distances between atoms in the molecules is clearly imprinted in the spatial interference patterns of this scattered wave. This phenomenon of electron scattering can also be described by quantum mechanics. Therefore in this section, we will first learn the framework of quantum mechanics for dealing with the scattering phenomenon. Then, after learning the mechanism of electron scattering caused by atoms, we will discuss the case of electrons being scattered by molecules and learn how molecular structures are reflected in the interference patterns of scattered electrons, thereby reaching an understanding of the method for determining molecular structures by the analysis of interference patterns. In addition, we will learn the effect of molecular vibration on interference patterns, and understand the difference between the molecular structure obtained from the analysis of rotational structure in spectra introduced in the previous chapter and that obtained from the gas electron diffraction method.