  We study the dynamical properties of the Mermin model, a simple quantum
dissipative model with a monochromatic environment, using analytical and
numerical methods. Our numerical results show that the model exhibits a second
order phase transition to a localized state before which the system is
effectively decoupled from the environment. In contrast to the spin-boson
model, the Mermin model exhibits an ``orthogonality catastrophe,'' defining the
critical point, before dissipation has destroyed all coherent behavior. An
analytic approach based on the Liouvillian technique, though successful in
describing the phase diagram of spin-boson and related models, fails to capture
this essential feature of the Mermin model.
