The ultrafast photodissociation dynamics of thionyl chloride after excitation with a 235 nm pump pulse has been studied using a femtosecond time-resolved mass spectroscopy.The observed parent transient suggests that the excited states initiated by 235 nm are very shortlived,that is,approximately 166 fs.Not only a stepwise three-body dissociation pathway but also a concerted three-body dissociation pathway is observed.
Experiments with the limited space-charge accumulation（LSA） mode of oscillation in a large gap semiinsulating （SI） GaAs photoconductive semiconductor switch（PCSS） are discussed.It has been observed that growth and drift of a photo-activated charge domain（PACD） are quenched only when the bias voltage is more than twice the threshold voltage.The original negative resistance characteristics are directly utilized in the LSA mode;during LSA operation the spatial average of the electric field varies over a large portion of the negative differential mobility region of the velocity-electric field characteristic.The work efficiency of an SI GaAs PCSS is remarkably enhanced by electric field excursions into the positive resistance region when the total electric field is only below the threshold part of the time.The LSA mode can only operate in the certain conditions that satisfy the quenching of the accumulation layer and the smaller initial domain voltage.
