  Classical results of Stieltjes are used to obtain explicit formulas for the
peakon-antipeakon solutions of the Camassa-Holm equation. The closed form
solution is expressed in terms of the orthogonal polynomials of the related
classical moment problem. It is shown that collisions occur only in
peakon-antipeakon pairs, and the details of the collisions are analyzed using
results {}from the moment problem. A sharp result on the steepening of the
slope at the time of collision is given. Asymptotic formulas are given, and the
scattering shifts are calculated explicitly
