Microwave lens effect for the J = 0 rotational state of CH₃CN

We demonstrate the manipulation of the translational motion of a polar molecule in its J = 0 rotational ground state by the microwave (MW) dipole force combined with a counter-rotating nozzle. A cold molecular beam of CH ₃CN seeded in Kr with a longitudinal velocity of about 100 m s ^-1 was created by a pulsed counter-rotating nozzle. The cold beam was then introduced into a cylindrical MW cavity, in which a standing wave, TM _01p mode MW field, nearly resonant to the |J, K〉 = |1, 0〉 ← |0, 0〉 rotational transition of CH₃CN was created. By choosing an appropriate MW frequency, we successfully observed focusing and deflection of the cold beam of CH₃CN due to the lens effect of the MW standing wave. The present result indicates that the combination of a counter-rotating nozzle and an MW cavity will be a versatile method for making cold and ultracold ensembles of various polar molecules in their rotational ground state.