Improved Momentum-Transfer Theory for Ion Mobility. 1. Derivation of the Fundamental Equation

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• 作者：William F. Siems ; Larry A. Viehland ; Herbert H. Hill ; Jr.
• 刊名：Analytical Chemistry
• 出版年：2012
• 出版时间：November 20, 2012
• 年：2012
• 卷：84
• 期：22
• 页码：9782-9791
• 全文大小：399K
• 年卷期：v.84,no.22(November 20, 2012)
• ISSN：1520-6882

文摘

For the first time the fundamental ion mobility equation is derived by a bottom-up procedure, with real atomic ion鈥揳tomic neutral collisions replaced by repetitions of an average collision. Ion drift velocity is identified as the average of all pre- and postcollision velocities in the field direction. To facilitate velocity averaging, collisions are sorted into classes that 鈥渃ool鈥?and 鈥渉eat鈥?the ion. Averaging over scattering angles establishes mass-dependent relationships between pre- and postcollision velocities for the cooling and heating classes, and a combined expression for drift velocity is obtained by weighted addition according to relative frequencies of the cooling and heating encounters. At zero field this expression becomes identical to the fundamental low-field ion mobility equation. The bottom-up derivation identifies the low-field drift velocity as ³/₄ of the average precollision ion velocity in the field direction and associates the passage from low-field to high-field conditions with the increasing dominance of 鈥渃ooling鈥?collisions over 鈥渉eating鈥?collisions. Most significantly, the analysis provides a direct path for generalization to fields of arbitrary strength.