  We prove a limiting absorption principle for a generalized Helmholtz equation
on an exterior domain with Dirichlet boundary conditions \begin{equation*}
  (L+\lambda)v=f,
  \qquad
  \lambda\in \mathbb{R}
  \end{equation*} under a Sommerfeld radiation condition at infinity. The
operator $L$ is a second order elliptic operator with variable coefficients,
the principal part is a small, long range perturbation of $-\Delta$, while
lower order terms can be singular and large. The main tool is a sharp uniform
resolvent estimate, which has independent applications to the problem of
embedded eigenvalues and to smoothing estimates for dispersive equations.
