Photodetachment from negative chlorine ions has been studied in the presence of a strong microwave field. Detachment near the single-photon threshold at 3.613 eV was observed by measuring the production of neutrals resulting from illumination of the ions by pulsed ultraviolet laser light and without microwaves. Microwaves with a frequenty of 2.6 GHz and maximum field strengths near 3 kV/cm produced results consistent with the assumption that each photodetachment event takes place in a constant electric field. No ponderomotive shift in the threshold was evident.

• Received 15 November 1989

DOI:https://doi.org/10.1103/PhysRevLett.65.1336