Collisional deactivation of ions

A tandem ion cyclotron resonance spectrometer was used, in which [C3H5]+ ion was formed from ethylene in the moderately high pressure ion source and then injected into the i.c.r. cell in order to react with the ethylene/bath gas mixture. Relative intensities of [C5H9]+ and [C5H7]+ were determined as a function of pressure in the i.c.r. cell. Knowledge of the neutral density and of the residence time of the ions in the i.c.r. section provides a means for evaluation of the average number of collisions encountered by the [C5H9]+ ions. Similar experiments were conducted with the perdeutero ion [C3D5]+, and neutral C2D4. Relative collisional stabilisation efficiency factors are given for 15 bath gases. The results are discussed and it is concluded that the use of the tandem i.c.r. gives a very close insight into the amount of energy actually transferred in ion-molecule collisions. (U.K.)