High-Resolution Diatomic Spectroscopy near the Dissociation Threshold

Current progress in and prospects for high-resolution molecular laser spectroscopy used for quantum-mechanical modeling of the energy and radiation properties of the rovibronic states of diatomic molecules near the dissociation threshold are discussed at the experimental (spectroscopic) level of accuracy, which is impossible without taking into account all types of intramolecular interactions. The weakly bound, quasibound, and continuum rovibronic states localized near the dissociation threshold actively participate in the formation of stable molecules during spontaneous or laser-stimulated association of colliding atoms, which leads to cooling of the initial reaction medium. Laser-induced fluorescence (LIF) combined with high-resolution Fourier transform spectroscopy is a unique experimental technique, which allows the study of all the three (bound, quasibound, and continuum) parts of the molecular spectrum simultaneously. LIF experiments combined with precision ab initio electronic structure calculations and global nonadiabatic analysis of quasidegenerate rovibronic states converging to the same dissociation limit make it possible to study the structural and dynamic properties of isolated molecules over a very wide range of their electronic-vibrational-rotational excitation.