Li Lei, Millay John T, Turner John P, King Fred L
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506-6286, USA.
J Am Soc Mass Spectrom. 2004 Jan;15(1):87-102. doi: 10.1016/j.jasms.2003.09.004.
The internal energy distributions, P(epsilon), of a millisecond pulsed radio frequency glow discharge plasma were investigated using tungsten hexcarbonyl W(CO)(6) as 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)(6) to construct the P(epsilon) plots. The P(epsilon) of W(CO)(6) exhibited 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(epsilon) 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(epsilon). These studies also provided insight into the correlation of the observed P(epsilon)s with the fundamental ionization and excitation mechanisms in the plasma. The temporal and spatial variations in P(epsilon) 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.
使用六羰基钨W(CO)₆作为“温度计分子”，研究了毫秒脉冲射频辉光放电等离子体的内能分布P(ε)。将探针分子W(CO)₆的蒸汽引入等离子体，并使其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产生的分子离子和碎片离子。将离子丰度数据与已知的W(CO)₆能量学相结合，构建P(ε)图。W(CO)₆的P(ε)在脉冲周期内表现出强烈的时间依赖性：在放电击穿期（预峰值）、稳态期（平台期）和脉冲后期（后峰值）发现了不同的内能分布。还观察到P(ε)的空间变化，尤其是在平台期。这些观察结果表明，这种脉冲辉光放电具有出色的能量可调性，可用于对分子、结构和元素信息进行选择性电离和碎片化。进行了参数研究，以评估放电压力和操作功率对P(ε)的影响。这些研究还深入了解了观察到的P(ε)与等离子体中基本电离和激发机制之间的相关性。因此，P(ε)的时间和空间变化归因于等离子体特定区域在特定时间主导能量转移过程的变化。这些数据将有助于未来优化该源用于化学形态分析的性能。
