The rate constants for recombination and exchange reactions in the Lindemann mechanism are studied using the flux correlation approach with a form of the Boltzmannized flux operator, which can simultaneously describe the Kubo and familiar half-split forms. Since the reaction is affected by third body (bath gas) collisions, the rate constant depends on how the Boltzmannized flux operator is chosen. We find that at very high pressure the rate constant for recombination process calculated by the linear response theory is considerably larger than that given by the half-split form. (C) 2003 Elsevier B.V. All rights reserved.