The reduced distribution function formalism of diffusion-influenced bimolecular reactions is generalized to incorporate a quantum-mechanical gating mode in the description. An analytical expression for the reaction rate coefficient: is obtained in the Laplace transform domain for a general initial condition, For a simple reaction model, the time-dependent reaction rate coefficient and the product yield are calculated numerically for two representative initial conditions. Dependence of the rate coefficient and the product branching ratio on various reaction parameters is discussed. (C) 1997 American Institute of Physics [S0021-9606(97)50247-9].