Evidence of virtual dipole-supported states in electron scattering by methyl chloride

A previously detected negative-ion dipole-supported state of CH3Cl is ident ified as a virtual state whose energy is about -30 mu eV at J = K = 0, wher e I and K are the rotational angular momentum and its component about the s ymmetry axis. For higher J and low K the S-matrix poles in the complex ener gy plane move off the real axis and typically do not correspond to quasibou nd states, i.e. there is no time delay in scattering. If K is close to I, t he S-matrix poles correspond to quasibound states and may appear as Feshbac h resonances.