  The rate constants for recombination and exchange reactions are calculated
using the flux correlation approach with a general form of the Boltzmannized
flux operator, which can simultaneously describe the Kubo and traditional
half-split forms. First, we consider an exactly solvable model, i.e., the free
particle case, in terms of a new scaling function. Next, as a non-trivial case,
we study the recombination and exchange reactions at very high pressure. Since
the rate constant is calculated by Laplace transform of the flux correlation
function, the result depends on how the Boltzmannized flux operator is chosen.
We find that a choice of the flux operator affects the rate constant
considerably. For the recombination reaction, the ratio of the rate constant in
the half-split form to that in the Kubo form approaches zero in the high
pressure limit.
