Energy Levels of a Diatomic Molecule in Gaseous Phase

Summary

This chapter deals with: the pure vibration movement of a diatomic molecule; its rotation movement in its equilibrium configuration (rigid rotor); and the vibration‐rotation coupling. It also describes the theoretical model developed for studying the IR spectra, which result from the transitions between the vibration‐rotation energy levels of diatomic molecules. The contact transformation method has been generalized in molecular physics to study the spectroscopy of molecules and consists of using the eigenfunctions of the harmonic oscillator corresponding to the zeroth‐order Hamiltonian of equation. Van Vleck's contact method is used to split the Hamiltonian into blocks so that the molecules' IR spectra can be studied. The transitions between the energy levels that result from the interaction between the molecule's dipole moment or the induced dipole moment and the IR electromagnetic radiation lead, respectively, to absorption and/or emission spectra of the molecule or to the molecule's Raman spectra.