Strong Field Ionization of 尾-Estradiol in the IR: Strategies To Optimize Molecular Postionization in Secondary Neutral Mass Spectrometry

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• 作者：Andrew Kucher ; Andreas Wucher ; Nicholas Winograd
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：November 6, 2014
• 年：2014
• 卷：118
• 期：44
• 页码：25534-25544
• 全文大小：495K
• ISSN：1932-7455

文摘

Strong field laser photoionization of 尾-estradiol in the 10¹³鈥?0¹⁵ W/cm² intensity range at wavelengths between 1200 and 2000 nm was examined for both evaporated gas phase molecules and neutral species sputtered from a solid surface under bombardment with 20 keV C₆₀⁺ ions. It is shown that the ionization efficiency is saturated at laser intensities of the order of 10¹³ W/cm², while laser-induced photofragmentation is found to strongly increase between 10¹³ and 10¹⁴ W/cm² and stay constant at higher intensities. These findings suggest a strategy to improve the postionization efficiency by defocusing the laser beam in order to sample a larger fraction of the sputtered plume, while at the same time optimizing the conditions for intact photoionization of the sputtered molecules. The results reveal a substantial enhancement of the signal of intact postionized molecular ions to a level an order of magnitude above that of the corresponding secondary ions. They also provide an experimental estimate of 鈭?.5 脳 10^鈥? as an upper bound for the ion fraction (secondary ion formation probability) of the sputtered molecules.