Wave-packet dynamics: Level-crossing-induced changes in momentum distributions

We study the changes appearing in Gaussian momentum distributions of quantum-mechanical wave packets after a traversal of a linear level crossing. The numerical results are discussed in terms of the semiclassical Landau-Zener theory. We observe a momentum filtering effect in nondissipative crossings. The results obtained from studies of dissipative level crossings suggest that one can obtain substantial changes in momentum distributions with these systems. The Landau-Zener theory provides qualitative understanding of the processes taking place in the dissipative level crossing.