Charge transfer of Si(4+) with helium

Cross sections for charge transfer of Si(4+) ions with neutral He are calculated over a wide range of thermal energies (10-10 to the 6th K). The results, obtained using the molecular description of the collision process, illustrate the necessity of using accurately determined potential energy surfaces and dynamic couplings in order to achieve a satisfactory degree of detail. The reverse reaction of ionization of Si(3+) by He is also investigated; the rate coefficient is found to be negligibly small except for very high temperatures (T approximately equal to or greater than 5 x 10 to the 5th K).