The article discusses the rotational spectra of diatomic molecules with a 3Σ electronic ground state, focusing on their energy levels and transitions. The rotational energy levels are determined by the rotational quantum number N and the total angular momentum quantum number J, which includes the electron spin. When the molecule has nuclei with non-zero spin, this is combined with J to form the total angular momentum F.
The energy levels are described by a Hamiltonian that includes spin-spin, spin-rotation, and rotational kinetic energy terms. These terms depend on the internuclear distance, leading to centrifugal distortion and vibration-rotation interactions. The vibrational state dependence is expressed through Dunham coefficients, with additional terms for centrifugal distortion and other interactions.
The article also discusses the selection rules for electric and magnetic dipole transitions, which allow the determination of molecular constants such as Bv, lv, gv, Dv, rv, and dv for different vibrational states. By combining data from multiple vibrational states, potential coefficients and expansion parameters can be derived. The hyperfine structure is also discussed, including magnetic hyperfine coupling constants b and c, which are derived from the Bohr magneton, nuclear magneton, and the coupling parameter gN.
Keywords: rotational spectra, diatomic molecules, angular momentum quantum number
