  In this paper we analyze a free quantum particle in a straight Dirichlet
waveguide which has at its axis two Dirichlet barriers of lengths $\ell_\pm$
separated by a window of length 2a. It is known that if the barriers are
semiinfinite, i.e. we have two adjacent waveguides coupled laterally through
the boundary window, the system has for any a>0 a finite number of eigenvalues
below the essential spectrum threshold. Here we demonstrate that for large but
finite $\ell_\pm$ the system has resonances which converge to the said
eigenvalues as $\ell_\pm\to\infty$, and derive the leading term in the
corresponding asymptotic expansion.
