The article presents introductory materials for the processes inside atoms and between atoms based on energy levels. Firstly, the particles which have a probability to interact with the other species are described. Among the interacting species, photon and electron are elementary particles. The energy of a photon is calculated depending on its frequency. Electron has only translational kinetic energy calculated by translational speed. For atoms and molecules, their total energy is a summation of translational, vibrational and rotational energies. There are many energy levels representing excited levels. If we consider an atom, the minimum energy above the ground level causes excitation and constitutes a free electron. When energy transmitted to atom exceed the ionization energy (series limit), a free ion is created. After ionization, particles can attain any energy level so they create a continuum. All energy levels correspond to a configuration of possible energy states, which is called as degeneracy. It can be defined as the number of different quantum states with the same energy. For electron, there are only two possible states resulting from electron spin. Atoms can have larger degeneracy values depending on their quantum states.
Energy levels are represented in eV unit which is the energy required to move an electron with an applied 1 V. Energy can be converted into electron temperature by dividing the Boltzmann constant. Atomic energy levels can be evaluated with a bound electron. This outer shell electron is named as optical electron. If there are two bound electrons, this state is called as dielectronic excitation. When the inner shell electrons get involved in an excitation, their energy probably exceeds the ionization level and they experience an unstable state. The excited electrons fall to the ground state by emitting a photon with the same energy level. This occurs in a very brief time, like in nanoscale. This state is called metastable. An electron can be added to the outer shell of an atom. The energy necessary to attach an electron is defined by the electron affinity. However, I am confused about the ground state and the energy input for a negative ion. I cannot understand that how the energy levels of a negative ion can be sketched. It seems like a negative energy but I should explore further the electron affinity.
The last part in the reading is describing the possible collisions. If the energies and the identities of the particles are the same for the initial and final states and momentum is conserved, then we call it as elastic collision. Otherwise, it is an inelastic (nonelastic) collision. Throughout the article, all the possible collisions are represented in a symbolic way and described verbally.
To sum up, this reading is very helpful to understand energy levels and particle interactions. It gives an insight about the statistical side of excitation and ionization by simply defining degeneracy and giving many examples.
Reference: Mitchner, Morton, and Charles H. Kruger. “Partially ionized gases.” (1973).
Course: AME 60637