High Temperature Laser Photolysis in Reflected Shock Waves : Pulse Generation of Radicals and Their Chemical Reactions

提出了一种在反射冲击波中产生自由基脉冲的新方法，用于测量高温下自由基-分子反应速率。用ArF（193 nm）或KrF（248 nm）强脉冲激光在反射激波中光解O_2、CO_2、NO、H_2S和C_2H_2。通过原子共振吸收光谱法测量诸如H、O和N原子的原子种类的浓度。通过使用该方法，获得了以下结果。(1)结果表明，O_2和CO_2在193 nm处的反射激波中通过振动激发态的吸收发生光分解。从v”=7的吸收光谱还表明，O_2在248 nm处也能发生光分解。测定了v”=2和7时O_2的振动弛豫速率。(2)本文首次在高温下直接测定了N+H_2反应的速率常数。(3)H+H_2S反应的速率常数与温度的关系为非Arrhenius关系。这种温度依赖性解释了过渡态理论的基础上的过渡态的量子力学计算。(4)用ArF激光光解C_2H_2产生C_2H自由基。首次在高温下直接测定了C_2H+C_2H_2和C_2H+H_2反应的速率常数。

A new method for the pulse generation of radicals in reflected shock waves has been developed to measure the rates of radical-molecule reactions at high temperatures. An intense pulse of ArF (193 nm) or KrF (248nm) laser was used to photolyze O_2, CO_2, NO, H_2S, and C_2H_2 in reflected shock waves. Concentrations of atomic species such as H, O, and N atoms were measured by atomic resonance absorption spectroscopy. By using this method, following results were obtained.(1) It has been shown that O_2 and CO_2 could be photodecomposed at 193 nm in the reflected shock waves via the absorption from vibrationally excited states. It was also shown that O_2 could be phtolysed even at 248 nm by the absorption from v"=7. Vibrational relaxation rates of O_2 in v"=2 and 7 were determined.(2) Rate constants for the reactions of N+H_2 were directly determined at high temperatures for the first time.(3) Non-Arrhenius temperature dependence of the rate constant was found for the H+H_2S reaction. This temperature dependence was explained by a transition state theory based on the quantum mechanical calculation of the transition state.(4) The C_2H radical was produced by ArF laser photolysis of C_2H_2 in reflected shock waves. The rate constants of C_2H+C_2H_2 and C_2H+H_2 reactions were directly determined at high temperatures for the first time.