Photon‐enhanced attachment can be used as a conduction‐control mechanism for diffuse discharge opening switches. This paper presents experimental results on photon‐enhanced attachment based on vibrational excitation of vinyl chloride using a line‐tunable CO2laser. Strong resistance increases and discharge turnoff have been observed in low‐current, externally sustained dc discharges. The influence of experimental parameters such as discharge pressure, attacher concentration, discharge voltage, and laser wavelength are presented.