  A Langevin canonical framework for a chiral two--level system coupled to a
bath of harmonic oscillators is developed within a coupling scheme different to
the well known spin-boson model. Thermal equilibrium values are reached at
asymptotic times by solving the corresponding set of non--linear coupled
equations in a Markovian regime. In particular, phase difference thermal values
(or, equivalently, the so--called coherence factor) and heat capacity through
energy fluctuations are obtained and discussed in terms of tunneling rates and
asymmetries.
