静电六极装置电场分布的数值计算方法及在N_2O分子转动态选择、取向中的应用

Numerical Method of Field Distribution in Hexapole and State-selection and Orietation of N_2O Molecules

阐述求解极性分子转动态选择及取向静电六极装置中势能分布、电场分布的数值计算方法.为了获得电场分布公式,需通过数值迭代求解势能满足的Laplace方程,获取数值分布点,通过数值分布点,由待定系数的多级展开势能解析表达式进行最小二乘拟合获得势能分布公式,由势能对空间向量的微分获得电场分布.分子在六极电场中的运行轨迹采用经典Newton方程描述,并通过四阶龙格—库塔方法(Four Order Runge-Kutta Method)实现数值求解,其中能量处理采用量子力学方法.应用此方法给出静电六极装置的电场分布公式,运用获得的电场分布公式计算和讨论电场对极性分子N2O的静电六极转动态选择、取向所带来的影响.

A numerical method is presented to calculate electric field, potential and motion trajectory of molecules in a hexapole for rotational state-selection and orientation of polar molecules. Potential distribution obeys Lapace equation, by which numerical distribution by points is obtained. Then points are fitted to analytical expressions of potential by lest square fitting. The coefficients in a finite-term series approximation for potential distribution are determined. Electric intensity is obtained by differential of the potential. In hexapole, classical trajectories of polar molecules are described by Newton＇s equations and solved with four order Runge-Kutta method. The rotational energies and Stark energies are solved by quantum mechanics. With electric field distribution formula, influences of field distribution on hexapole rotational state-selection and orientation of N2O molecules are discussed.