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首页> 外文期刊>The Journal of Chemical Physics >Photochemical formation of HCO and CH3 on the ground S-0 ((1)A(')) state of CH3CHO
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Photochemical formation of HCO and CH3 on the ground S-0 ((1)A(')) state of CH3CHO

机译：H3和CH3在CH3CHO的S-0（（1）A（'））基态上的光化学形成

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摘要

The dynamics of the photodissociation of CH3CHO into CH3+HCO products have been investigated at energies between 30 953 and 31 771 cm(-1), spanning the threshold for radical production on the triplet (T-1) surface. A barrierless pathway to CH3+HCO radical products formed on the ground state (S-0) surface was discovered and established to be an important reaction channel in acetaldehyde photodissociation throughout this wavelength range. HCO laser induced fluorescence (LIF) spectra recorded from CH3CHO dissociated above and below the T-1 barrier energy are quite different; HCO produced on S-0 yields a more congested LIF spectrum with sharp rotational transitions, while HCO formed on the T-1 surface displays fewer, more intense, Doppler-broadened lines. These differences have been further explored in the populations of the HCO K-a=1 doublets. Despite the upper and lower levels being almost isoenergetic, HCO formed on T-1 preferentially populates the upper K-c state due to the geometry of the T-1 transition state structure. In contrast, HCO formed on S-0 produces equal population in each of the upper and lower K-a=1 components. Product state distributions (PSDs) showed that HCO formed on S-0 is born with an approximately statistical distribution of population in the available product states, modeled well by phase space theory. HCO formed on the T-1 surface, in contrast, has a PSD that can be characterized as arising from "impulsive" dynamics. Previous discrepancies in the height of the T-1 barrier are discussed following the observation that, once the T-1 channel is energetically accessible, there is competition between the S-0 and T-1 pathways, with the dominance of the triplet channel increasing with increasing photolysis energy.
机译：CH3CHO到CH3 + HCO产品的光解离动力学已在30 953和31 771 cm（-1）之间的能量下进行了研究，跨越了三重态（T-1）表面上自由基产生的阈值。发现并形成了在基态（S-0）表面上形成的CH3 + HCO自由基产物的无障碍途径，并被确定为在整个波长范围内乙醛光解离的重要反应通道。从CH3CHO记录的HCO激光诱导的荧光（LIF）光谱在T-1势垒能的上下分离。在S-0上产生的HCO产生更拥挤的LIF光谱，具有急剧的旋转跃迁，而在T-1表面上形成的HCO显示更少，更强烈，多普勒增宽的谱线。这些差异已在HCO K-a = 1的双峰态中进一步探讨。尽管上层和下层几乎是等能量的，但由于T-1过渡态结构的几何形状，在T-1上形成的HCO优先填充上K-c态。相反，在S-0上形成的HCO在上K-a = 1和下K-a = 1的每个分量中产生相等的种群。产品状态分布（PSDs）表明，在S-0上形成的HCO出生时在可用产品状态中具有大致统计的种群分布，并通过相空间理论很好地建模。相反，在T-1表面上形成的HCO具有PSD，其特征可以归因于“脉冲”动力学。在观察到以下问题之后，我们讨论了T-1障碍物高度的先前差异：观察到，一旦T-1通道可通过能量进入，则S-0和T-1途径之间就会发生竞争，三重态通道的优势会增加随着光解能量的增加。

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