Exact S matrix of the deformed c=1 matrix model

We consider the c=1 matrix model deformed by the operator 1/2M Tr-2, which was conjectured by Jevicki and Yoneya to describe a two-dimensional black hole of mass M. We calculate the exact nonperturbative S matrix and show that all the amplitudes involving an odd number of particles vanish at least to all orders of perturbation theory. We conjecture that these amplitudes vanish nonperturbatively and prove this for the 2n1 scattering. For the two- and four-particle amplitudes we give some leading terms of the perturbative expansion.