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首页> 外文期刊>The Journal of Chemical Physics >Photodissociation and photoionization of 2,5-dihydroxybenzoic acid at 193 and 355 nm
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Photodissociation and photoionization of 2,5-dihydroxybenzoic acid at 193 and 355 nm

机译：2,5-二羟基苯甲酸在193和355 nm处的光解离和光电离

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摘要

Photodissociation and photoionization of 2,5-dihydroxybenzoic acid (25DHBA), at 193 and 355 nm were investigated separately in a molecular beam using multimass ion imaging techniques. Two channels competed after excitation by one 193 nm photon. One channel is dissociation from the repulsive excited state along O-H bond distance, resulting in H atom elimination from meta-OH functional group. The other channel is internal conversion to the ground state, followed by H_2O elimination. Some of the fragments further proceeded to secondary dissociation. On the other hand, absorption of one 355 nm photon gave rise to H_2O elimination channel on the ground state. Absorption of more than one 355 nm photon resulted in the three-body dissociation which also occurs on the ground state. Dissociation on the excited state does not play a role at 355 nm. The large concentration ratio (2 × 105), between neutral fragments and cations produced from 355 nm multiphoton excitation indicates that internal conversion followed by dissociation, is the major channel for 355 nm multiphoton excitation. Multiphoton ionization is a minor channel. Multiphoton ionization of 25DHBA clusters only produces 25DHBA cations. Neither anion nor protonated 25DHBA cation were observed. It is very different from the ions produced from solid matrix-assisted laser desorptionionization (MALDI), experiments. This suggests that protonated 25DHBA and negatively charged 25DHBA generated in MALDI experiments does not simply result from the ionization following proton transfer reactions or charge transfer reactions of the clusters in the gas phase.
机译：在分子束中使用多质量离子成像技术分别研究了在193和355 nm处的2,5-二羟基苯甲酸（25DHBA）的光解离和光电离。激发后，两个通道竞争一个193 nm光子。一个通道是沿着O-H键距离从排斥的激发态解离，导致H原子从间位OH官能团中消除。另一个通道是内部转换为基态，然后消除H_2O。一些片段进一步进行了二级解离。另一方面，一个355 nm光子的吸收在基态上产生了H_2O消除通道。吸收超过一个355 nm光子会导致三体解离，这也发生在基态上。激发态的离解在355 nm处不起作用。 355 nm多光子激发产生的中性碎片与阳离子之间存在较大的浓度比（2×105），表明内部转化和解离是355 nm多光子激发的主要通道。多光子电离是次要通道。 25DHBA簇的多光子电离只能产生25DHBA阳离子。既未观察到阴离子，也未观察到质子化的25DHBA阳离子。它与固体基质辅助激光解吸（MALDI）实验产生的离子完全不同。这表明在MALDI实验中生成的质子化的25DHBA和带负电荷的25DHBA并非简单地由气相中质子转移反应或团簇的电荷转移反应后的电离引起。

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