Photodissociation of a surface-active species at a liquid surface: A study by time-of-flight spectroscopy
Photodissociation of a surface-active species at a liquid surface: A study by time-of-flight spectroscopy
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DOI：
10.1021/jp984054v
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发表时间：
1999-03-04
影响因子：
3.3
通讯作者：
Furlan, A
中科院分区：
文献类型：
--
作者：
Furlan, A
利用飞行时间/四极杆质谱（TOF/QMS）研究了气液界面的光化学反应。用波长为275 nm的纳秒激光脉冲照射溶解在甘油中的4-碘苯甲酸（IBA）的液体薄膜。原子和分子碘是在低通量激光脉冲（99%）后离开液体的唯一光产物。与此相反，T原子从IBA/甘油解吸是超热的（T-transs = 480 K），几乎完全起源于最顶层的分子层（1 nm）。TOF测量与快速斩波轮在前面的表面提供的时间依赖性的解吸通量从表面和确认，从更深的层在烷基碘溶液中的贡献是远远大于芳基碘溶液。模型计算预测的行为的两种解决方案正确的，如果考虑到在笼子里的成对的自由基，自由基的扩散系数的差异，和一套散装自由基反应在两种解决方案。根据激发态IBA分子的表面取向讨论了从IBA溶液中喷射出的I原子的超热能。飞行时间光谱对激光功率和IBA浓度的依赖性被解释为表面过量的IBA。将结果与IBA在甘油和水中的溶液的温度依赖性表面张力测量进行比较。表面张力对IBA在表面的积累的响应非常弱。
The photochemistry at a gas-liquid interface was investigated by time-of-flight/quadrupole mass spectroscopy (TOF/QMS). A thin liquid film of 4-iodobenzoic acid (IBA), dissolved in glycerol, was irradiated with nanosecond laser pulses at 275 nm. Atomic and molecular iodine were the only photoproducts leaving the liquid after a low-fluence laser pulse (99%). In contrast, T atoms desorbing from IBA/glycerol are hyperthermal (T-trans = 480 K) and originate almost exclusively from the topmost molecular layer (1 nm). TOF measurements with a fast chopper wheel in front of the surface provide the time-dependent desorption flux from the surface and confirm that the contribution from deeper layers in the alkyl iodide solution is much larger than in the aryl iodide solution. Model calculations predict the behavior of the two solutions correctly if differences in caging of the geminate pair, diffusion coefficients of the free radicals, and the set of bulk radical reactions in the two solutions are taken into account. The hyperthermal energies of the ejected I atoms from the IBA solution are discussed in terms of the surface orientation of excited IBA molecules. The dependence of the TOF spectra on laser power and IBA concentration is interpreted by a surface excess of IBA. The result is compared to temperature-dependent surface tension measurements of IBA solutions in glycerol and water. The response of the surface tension to an accumulation of IBA at the surface is very weak.