We have calculated the vibrational and rotational autoionization rate constants for diatomic molecules H 2 , N 2 , and HCl in high Rydberg states by employing the density matrix formulation with the inverse Born–Oppenheimer approximation basis set. The purpose is to simulate the main radiationless processes occurring in zero electron kinetic energy (ZEKE) spectroscopy. The quantum numbers and the energy dependences of the calculated autoionization rate constants are represented as the scaling laws via nonlinear regression. These data provide a suitable starting point for quantitative study of the intricate dynamics involved in ZEKE Rydberg states.