A general theoretical procedure to analyze the characteristics and dynamics of superexcited states of diatomic molecules is developed. It utilizes the following three methods effectively: (I) quantum chemical methods to evaluate basic parameters of the superexcited states, (2) spectroscopic experiments to improve the basic information obtained theoretically, and (3)multi-channel quantum defect theory (MQDT) to analyze couplings among various kinds of states and to clarify the dynamics. This procedure is composed of seven steps, including a method to evaluate the electronic coupling of the first kind of superexcited state to ionization continuum which is newly proposed here. The two-center Coulomb function in the field of the corresponding diatomic molecular ion is used to evaluate this coupling. This can be done by incorporating the Coulomb functions into an ab initio quantum chemical code. The whole procedure is illustrated for the CO molecule. (C) 1997 American Institute of Physics.