Inelastic Scattering of CN Radicals at the Gas-Liquid Interface Probed by Frequency-Modulated Absorption Spectroscopy
Inelastic Scattering of CN Radicals at the Gas-Liquid Interface Probed by Frequency-Modulated Absorption Spectroscopy
复制标题
调频吸收光谱探测CN自由基在气液界面的非弹性散射
DOI：
10.1021/acs.jpcc.0c04023
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Lane P
中科院分区：
文献类型：
--
作者：
Lane P
我们描述了调频吸收光谱首次应用于气液界面的分子散射动力学的结果。利用脉冲直流电放电在He中植入BrCN的超音速膨胀，产生了旋转冷CN（X2Σ+）自由基的脉冲分子束，其实验室框架平均动能为43.5 kJ mol-1。分子束以正入射方向定向到不断刷新的全氟聚醚液体表面。利用CN(A2Π-X2Σ+)（2,0）波段上的调频吸收光谱测量了直流放电脉冲后CN各旋转状态的多普勒谱线形状随时间的变化。这使得入射分子束和非弹性表面散射CN旋转和平移能量分布的表征成为可能。在850±130 K的单一温度下，表面散射的CN旋转分布具有良好的特征。垂直于表面法线的平动分布是非麦克斯韦分布，基本上是过热分布。我们将这些观测结果解释为脉冲散射是主要机制的结果，类似于我们之前在液体表面对OD非弹性散射的独立测量。在目前的信噪比限制下，与之前文献中对全氟聚醚表面上no和co2散射的测量结果相比，没有明确的证据表明热解吸中存在离散成分。
We describe the results of the first application of frequency-modulated (FM) absorption spectroscopy to molecular scattering dynamics at a gas–liquid interface. A pulsed direct-current (dc) electric discharge of a supersonic expansion of BrCN seeded in He was used to generate a pulsed molecular beam of rotationally cold CN(X2Σ+) radicals with a mean laboratory-frame kinetic energy of 43.5 kJ mol–1. The molecular beam was directed at normal incidence onto a continually refreshed perfluoropolyether liquid surface. FM absorption spectroscopy on the CN(A2Π-X2Σ+) (2,0) band was used to measure Doppler line shapes for individual CN rotational states as a function of time after the dc discharge pulse. This enabled characterization of both the incident molecular beam and the inelastically surface-scattered CN rotational and translational energy distributions. The surface-scattered CN rotational distribution is well characterized by a single temperature of 850 ± 130 K. The translational distributions perpendicular to the surface normal are non-Maxwellian and are substantially superthermal. We interpret these observations as the result ofimpulsive scatteringbeing the dominant mechanism, similar to our previous independent measurements of OD inelastic scattering at liquid surfaces. Within the current limitations of signal to noise, no clear evidence for a discrete component fromthermal desorptionis observed, in contrast to previous literature measurements of NO and CO2scattering at perfluoropolyether surfaces.