We consider a one-dimensional molecule with a permanent electric dipole moment incident along the
line of symmetry of a circular hole in an infinite two-dimensional conducting sheet. We calculate
the probabilities of reflection p R and transmission p T of a centre of mass wave packet initially
of the form of a Gaussian wave packet and moving toward the hole. We show the dependence of p T and
p R on the charge Q of the atoms, the radius a of the hole as compared to the length scale ##IMG##
[http://ej.iop.org/images/0143-0807/38/1/015403/ejpaa45f9ieqn1.gif] {$1/\alpha $} of the bound
molecular relative motion state, the mass and energy of the molecule. We compare a fully quantum
mechanical treatment to a semiclassical approximation in which the distance between the atoms is
constant. Some unexpected and surprising results emerge from this study.