EXACT S-MATRIX OF THE DEFORMED C = 1 MATRIX MODEL

We consider the c = 1 matrix model deformed by the operator 1/2 M TrPH I-2, which was conjectured by Jevicki and Yoneya to describe a two-dim ensional black hole of mass M. We calculate the exact nonperturbative S matrix and show that all the amplitudes involving an odd number of p articles vanish at least to all orders of perturbation theory. We conj ecture that these amplitudes vanish nonperturbatively and prove this f or the 2n --> 1 scattering. For the two- and four-particle amplitudes we give some leading terms of the perturbative expansion.