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 pR and transmission pT 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 pT and pR on the charge Q of the atoms, the radius a of the hole as compared to the length scale
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.