In our previous experimental [Chem. Phys. Lett. 365 (2002) 244] and theoretical [Chem. Phys. Lett. 371 (2003) 342] studies, quantum interference on collision-induced rotational energy transfer of CO (A(1)Pi, v = 3) with inert gases, which originates from the difference between the two Lambda-related collision potential energy surfaces is reported. The interference angle, which measures the degree of coherence, is presented in this Letter. Based on the time-dependent first-order Born approximation, taking into account the anisotropic Lennard-Jones interaction potentials, the factors (experimental temperature, partner and rotational quantum number) that the interference angle depends on are obtained. For the homonuclear diatomic, the case of the 'complete interference' under some approximation is derived. For the hetero-nuclear diatomic, degree of the interference with the factors is discussed. (C) 2003 Elsevier Science B.V. All rights reserved.