  We develop the analytical method of field momenta for analyzing the dynamics
of optical vector solitons in photorefractive nonlinear media. First, we derive
the effective evolution equations for the parameters of multi-component
solitons composed of incoherently coupled beams and investigate the soliton
internal oscillations associated with the relative motion of the soliton
components. Then, we apply this method for analyzing the vector soliton
scattering by a nonlinear interface. In particular, we show that a vector
soliton can be reflected, transmitted, captured, or split into separate
components, depending on the initial energy of its internal degree of freedom.
The results are verified by direct numerical simulations of spatial optical
solitons in photorefractive nonlinear media.
