PATHWAYS AND KINETIC-ENERGY DISPOSAL IN THE PHOTODISSOCIATION OF NITROBENZENE
PATHWAYS AND KINETIC-ENERGY DISPOSAL IN THE PHOTODISSOCIATION OF NITROBENZENE
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DOI：
10.1063/1.464188
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发表时间：
1993-02-01
影响因子：
4.4
通讯作者：
CRIM, FF
中科院分区：
文献类型：
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作者：
GALLOWAY, DB;BARTZ, JA;CRIM, FF
真空紫外光解离分子束质谱法是一种鉴定初级光解产物和测定其反冲能的方法。在220 ~ 320 nm的光解波长范围内，我们观察到硝基苯的三个主要光解途径。其中两种途径是C6H5NO2—> C6H5 + NO2和C6H5NO2—> C6H5NO + o。第三种途径通过C6H5NO2—> C6H5O + NO和C6H5NO2—> C5H5 + CO + NO的一个或两个过程产生NO。产生NO2和NO的途径的相对产率随光解波长变化很大。在280 nm的光解过程中，NO2的产量超过NO的50%，但在222 nm的光解过程中，NO2的产量几乎增加到6倍。第二种途径的阈值能量大约比由硝基苯生成硝基苯（C6H5NO）和一个氧原子的热力学极限大0.50 eV，这可能反映了生成三态硝基苯所需的能量，也可能是三态表面的解离屏障。碎片到达时间的分布提供了这些实验中每个光解波长的反冲能量的估计。产生一氧化氮（NO）自由基的通道释放出相对较大的动能。假设产生一氧化氮（NO）的通道也产生苯氧基（C6H5O），我们计算出动能从320 nm处的0.29 eV线性增加到220 nm处的1.1 eV。相比之下，其他两个通道在所有波长下仅释放少量动能（几乎等于= 0.1 eV）。脉冲模型不能描述这些低能量通道的动能释放，这表明能量释放更接近于统计。由脉冲模型预测的产生一氧化氮和苯氧自由基的通道的反冲能量与观察到的动能释放更接近。
Vacuum-ultraviolet photoionization molecular-beam mass spectrometry is a means of identifying primary photodissociation products and determining their recoil energies. At several photolysis wavelengths between 220 and 320 nm, we have observed three primary photodissociation pathways for nitrobenzene. Two of the pathways are C6H5NO2 --> C6H5 + NO2 and C6H5NO2 --> C6H5NO + O. The third pathway produces NO by one or both of the processes C6H5NO2 --> C6H5O + NO and C6H5NO2 --> C5H5 + CO + NO. The relative yield of the pathways producing NO2 and NO varies strongly with the photolysis wave-length. The production of NO2 exceeds that of NO by about 50% for the 280 nm photolysis, but increases to almost a sixfold excess in 222 nm dissociation. The second pathway has a threshold energy that is about 0.50 eV greater than the thermodynamic limit for the formation of nitrosobenzene (C6H5NO) and an oxygen atom from nitrobenzene, probably reflecting the energy required to produce triplet nitrosobenzene and, perhaps, a barrier to dissociation on the triplet surface. The distribution in arrival times for a fragment provides an estimate of the recoil energy at each photolysis wavelength in these experiments. The channel producing nitric oxide (NO) radicals releases a relatively large amount of kinetic energy. Assuming the channel producing nitric oxide (NO) also produces phenoxy (C6H5O), we calculate a linear increase in kinetic energy from 0.29 eV at 320 nm to 1.1 eV at 220 nm. By contrast, the other two channels release only a small amount of kinetic energy (almost-equal-to = 0.1 eV) at all wavelengths. An impulsive model does not describe the observed kinetic energy release for these low energy channels, suggesting that the energy release is more nearly statistical. The recoil energy predicted by an impulsive model for the channel producing nitric oxide and phenoxy radicals is closer to the observed kinetic energy release.