Elastic and inelastic cross-sections of the mercury atom

A considerable amount of experimental work has been done in investigating the total cross-section of an atom for collision with an electron in various gases. The total cross-section is measured by determining the number of electrons deflected out of a homogeneous beam, or which have their energy decreased, as the beam passes through the gas. For a complete knowledge of collision processes, it is necessary to know not only the total cross-section for collision but also the cross-section of the atom for various specific types of collision. The total cross-section can be divided into two main partial cross-sections—that for elastic collision and that for inelastic collision. The latter may be subdivided into the cross-section for excitation and the cross-section for ionization. The cross-section for excitation may then be further subdivided into the various cross-sections pertaining to the numerous discrete energy losses that the electron may suffer in its collision with the atom.