Department of Chemistry, Purdue University, 47907, West Lafayette, Indiana, USA.
J Am Soc Mass Spectrom. 1993 Oct;4(10):792-7. doi: 10.1016/1044-0305(93)80037-Y.
The effects on ion motion caused by the application of a resonance AC dipole voltage to the end-cap electrodes of the quadrupole ion trap are described. An excimer laser is used to photodissociate benzoyl ions, and its triggering is phase locked to the AC voltage to follow the motion of the ion cloud as a function of the phase angle of the AC signal. Resonantly excited ions maintain a coherent motion in the presence of He buffer gas, which dissipates energy from the ions via collisions. Maximum ion displacements, which depend upon the potential well depth (q z value), occur twice each AC cycle. Axial components of ion velocities are determined by differentiating the displacements of the distributions with respect to time. The experimental data show that these velocities are maximized when the ion cloud passes through zero axial displacement, and they compare favorably with results calculated using a simple harmonic oscillator model. Axial components of ion kinetic energies are low (<5 eV) under the chosen experimental conditions. At low values of q2 (≈ 0.2), the width of the ion distribution increases as the ion cloud approaches the center of the trap and decreases as it approaches the end-cap electrodes. This effect is created by compaction of the ion trajectories when ion velocities are decreased.
本文描述了在四极离子阱的端盖电极上施加共振交流偶极电压对离子运动的影响。采用准分子激光器将苯甲酰离子光解，并将其触发与交流电压进行相位锁定，以随交流信号的相位角跟踪离子云的运动。在氦缓冲气体存在的情况下，共振激发的离子保持相干运动，通过碰撞耗散离子的能量。最大离子位移取决于势阱深度（qz 值），每个交流周期出现两次。通过对分布相对于时间的位移进行微分来确定离子速度的轴向分量。实验数据表明，当离子云通过零轴向位移时，这些速度达到最大值，并且与使用简单谐振子模型计算的结果相比非常吻合。在所选实验条件下，离子动能的轴向分量较低（<5 eV）。在 q2 值较低（≈0.2）的情况下，当离子云接近阱中心时，离子分布的宽度增加，当它接近端盖电极时，宽度减小。当离子速度降低时，这种效应是通过压缩离子轨迹而产生的。
