Shock Tube-TOF Mass Spectrometer Apparatus with Cryosorption Pumping

In sampling reflected shock waves directly into a time-of-flight mass spectrometer, one of the crucial problems is to remove the sampled gas from the ion source. Preliminary experiments with the mass spectrometer flight tube and shock tube axis collinear showed that more pumping speed was required to cope with the sample jet. The required pumping rate, estimated from the rate of pressure decrease on the high pressure side of the sampling orifice, was of the order of 105 liter/sec at 10−6 Torr. A cryosorption pump was built which employed a freshly evaporated molybdenum film at liquid nitrogen temperature as the pumping surface. The shock tube and flight tube axes were placed perpendicular and the sample beam passed through the ionizing electron beam into the cryosorption pump. This arrangement proved satisfactory, and results on the decomposition of CS2 were in reasonable agreement with those of other workers.