Time-resolved ion cyclotron resonance

Ion cyclotron resonance (i.c.r.) is a technique for the study of ion-molecule reactions in the collisional range from thermal to several electron volts. The study of these reactions at low energy has been given impetus by the discovery of their importance in the ionosphere and in interstellar space. This communication identifies some possible weaknesses inherent in current i.c.r. work and suggests an improved technique with which it is possible to determine absolute rate constants more reliably. As an illustration of the technique a measurement of the rate constant for the reaction CH4+ + CH4 → CH5+ + CH3 is presented. This value is k = 1.21 + - 0.09 x 10-15 m3 s-1. A new i.c.r. cell design is discussed with which it is hoped to provide further improvement in reliability by the production of a homogeneous radiofrequency field within a true quadrupole trap. (author)