Study of Charge Transfer Collision of N²⁺ with N₂ in an RF Ion Trap

The charge-transfer rate coefficients for reaction M²⁺ （2^s2p, ²P⁰）+N₂→ products is measured by recording the the dependence of the M²⁺ stored in an ion trap. A quadrupole radio-frequency ion trap was used to trap N²⁺ produced by electron bombardment,With operating the trap near the cross point of β_z=1 and β_r=0 of the first stability region （i.e. the operating point of a_z=0.15, q_z=0.78）, N²⁺ with equilibrium energy of about 1.4 eV have been seledively confined in the trap.
After the mass selective storage and charge transfer collision processes the produced ions have been ejectal from the trap and detected. The dacay of the N²⁺ signals was analyzed by single exponential least-squares fits to the data, the obtained decay rates represented corresponding charge-transfer rates. We repeatal these measurements under five different reactant gas N₂ pressures and obtained the variation of the charge-transfer rates versus the N₂ pressures.The charge-transfer rate coefficient have ho evaluated to be 1.89 （0.56）×10^-9cm³s^-1.The uncertainty presental here is due to the uncertainty of the gas pressure measurernents and the uncertainty of the ion signal intensity resulted from the fluctuation of laser power and other nonlinear effects of the detection circuit.
Our measured result is in good agreement with theoretical Langevin rate coefficient of 2.6×^-9cm³s^-1. It is also in agreement with Kwong’s experimental value of 2.1 （0.18）×^-9cm³s^-1 measured in a cylindrical RF ion trap at equilibrium energy of 2.7eV, and is consistent with Church’s early published value of 2.8 （0.6）×10^-9cm³s^-1 obtained in a Penning trap with equilibrium energy larger than 3eV.