We prove a version of the Feynman-Kac formula for Levy processes and
integro-differential operators, with application to the momentum representation
of suitable quantum (Euclidean) systems whose Hamiltonians involve
L\'{e}vy-type potentials. Large deviation techniques are used to obtain the
limiting behavior of the systems as the Planck constant approaches zero. It
turns out that the limiting behavior coincides with fresh aspects of the
semiclassical limit of (Euclidean) quantum mechanics. Non-trivial examples of
Levy processes are considered as illustrations and precise asymptotics are
given for the terms in both configuration and momentum representations