NOVEL TECHNIQUE FOR REAL-TIME MONITORING OF ELECTRON-ATTACHMENT TO LASER-EXCITED MOLECULES

We report a new experimental technique that is capable of monitoring e lectron attachment to laser-excited molecules in real time; the time r esolution is limited only by the time constant of the detection circui t and was similar to 100 ps for the experiments reported here. This te chnique provides information on the lifetime of the excited states res ponsible for electron attachment, and also allows determination of ele ctron attachment cross sections involved. Results on dissociative elec tron attachment to ArF-excimer-laser-irradiated NO are reported: Elect ron attachment occurred to the A (2) Sigma(+)(nu=3) state populated vi a the absorption of a single photon, and to highly excited states popu lated via two-photon absorption; the cross section for low-energy elec tron attachment to the A (2) Sigma(+)(nu=3) state was similar to 3 ord ers of magnitude larger compared to that for the A (2) Sigma(+)(nu=0). Decay of the electrons over the similar to 200 ns lifetime of the A ( 2) Sigma(+)(nu=3) state was directly monitored. Negative-ion formation that occurred via the A (2) Sigma(+)(nu=3) state was suppressed in th e presence of CO2 due to collisional quenching of that state by CO2, a nd the reduction in the A (2) Sigma(+)(nu=3) state lifetime with incre asing CO2 pressure was also observed. (C) 1996 American Institute of P hysics.