Some ion-molecule reaction rate coefficient measurements at 300 and 100K in a temperature-variable flowing-afterglow apparatus

A temperature-variable flowing-afterglow apparatus (100-300K) has been used to measure a number of ion-molecule reaction rate coefficients. These include He + +N 2 O, N + +O 2 , O + +O 2 , C + +O 2 , C + +CO 2 and N 2 H + +CO 2 . Measurements at low temperatures are less straightforward than in a room temperature system because of the much lower Penning reaction rate coefficients at the lower temperatures. Helium 2 3 S metastables give rise to unwanted ion generation along the flow tube. This problem has been overcome by using a long path length between ion source and reaction region so that all the helium metastables have been destroyed before the primary ions reach the reaction region. The success of this procedure is confirmed by the good linear plots obtained.