Millisecond pulsed radio frequency glow discharge time of flight mass spectrometry: Temporal and spatial variations in molecular energetics
Millisecond pulsed radio frequency glow discharge time of flight mass spectrometry: Temporal and spatial variations in molecular energetics
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毫秒脉冲射频辉光放电飞行时间质谱：分子能量学的时间和空间变化
DOI：
10.1016/j.jasms.2003.09.004
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发表时间：
2003
影响因子：
3.2
通讯作者：
F. L. King
中科院分区：
文献类型：
--
作者：
Lei Li;J. T. Millay;John J. P. Turner;F. L. King
以碳化钨W(CO)6为“温度计分子”，研究了毫秒脉冲射频辉光放电等离子体的内部能量分布P(ɛ)。探针分子W(CO)6的蒸气被引入到等离子体中，并在其中经历各种电离和激发过程。使用飞行时间质谱仪监测生成的分子和碎片离子。利用离子丰度数据结合W(CO)6的已知能量学建立了P(ɛ)图。W(CO)6的P(ɛ)在脉冲周期内表现出强烈的时间依赖性：在放电击穿阶段(峰前)、稳态期(平台)和脉冲后阶段(峰后)发现了不同的内部能量分布。P(ɛ)的空间变化也被观察到，尤其是在高原地区。观察表明，这种脉冲辉光放电提供了极好的能量可调性，可用于对分子、结构和元素信息进行选择性电离和碎裂。通过参数研究评估了放电压力和操作功率对P(ɛ)的影响。这些研究也为观测到的P(ɛ)S与等离子体中的基本电离和激发机制之间的关系提供了新的见解。因此，P(ɛ)的时间和空间变化归因于等离子体特定区域在特定时间的主导能量传递过程的变化。这些数据将有助于今后努力优化这一化学形态来源的分析性能。
The internal energy distributions, P(ɛ), of a millisecond pulsed radio frequency glow discharge plasma were investigated using tungsten hexcarbonyl W(CO)6as a “thermometer molecule”. Vapor of the probe molecule, W(CO)6, was introduced into the plasma and subjected to various ionization and excitation processes therein. The resultant molecular and fragment ions were monitored using a Time-of-Flight mass spectrometer. Ion abundance data were utilized in combination with the known energetics of W(CO)6to construct the P(ɛ) plots. The P(ɛ) of W(CO)6exhibited strong temporal dependence over the pulse cycle: Distinct internal energy distributions were found at the discharge breakdown period (prepeak), the steady state period (plateau), and the post-pulse period (afterpeak). Spatial variation in P(ɛ) was also observed, especially during the plateau regime. The observations suggest that this pulsed glow discharge affords excellent energy tunability that can be used to perform selective ionization and fragmentation for molecular, structural, and elemental information. Parametric studies were performed to evaluate the effects of discharge pressure and operating power on P(ɛ). These studies also provided insight into the correlation of the observed P(ɛ)s with the fundamental ionization and excitation mechanisms in the plasma. The temporal and spatial variations in P(ɛ) were hence attributed to changes in the dominant energy transfer processes at specific times in specific regions of the plasma. These data will be useful in future efforts to optimize the analytical performance of this source for chemical speciation.