On the theta divisor of SU(2,1)

Let SU(2,1) be the moduli space of stable rank two vector bundles having fixed determinant of odd degree over a compact Riemann surface C. In this paper it is shown that the Theta divisor of SU(2,1) is very ample for every C. The proof is related to the study of the base locus of the pencil of divisors 2-theta in the Jacobian of C which is naturally associated to a point of SU(2,1).