在Kr-Azulene碰撞中能量轉移之研究

Abstract

本研究中利用classical trajectory simulation的方式來模擬高激發振動態的azulene和Kr之間碰撞後的能量轉移。最近由中央研究院原分所的倪其焜教授所率領的團隊對此系統進行單一碰撞尺度實驗研究。在碰撞能量分別為170 cm-1，410 cm-1，和780 cm-1的情況下,於他們的研究當中發現有1%到0.3%的supercollision的存在。即使只有微量存在，supercollision對於像是反應速率這類的性質之影響是很大的。因此在本研究當中便對如何形成supercollision的機制做了探討。為了能夠有效能夠模擬碰撞過程，本研究利用來自MP2/6-31G**計算方式所得出來的結果來建構一個足以描述Kr和Azulene之間作用力的位能面(potential energy surface)，對於能支配Azulene分子內部能量流動的作用力，則是利用文獻中可以得出Azulene的振動頻率的位能來描述。對計算後的結果進行深入的研究，發現有三種可形成supercollision的機制,分別為錯合物機構 (The complex mechanism)，二次撞擊機制(The double hit mechanism)和一次撞擊機制(The single hit mechanism)。同時也發現在低的碰撞能量下，錯合物機制對於supercollision的影響和其他機制一樣重要，然而隨著碰撞能量的增加，錯合物機制的影響則會大大的減少。In this thesis, the energy transfer between highly vibrationally excited azulene (Az, C10H8) and krypton atoms is studied using classical trajectory simulations. Recently, this system has been studied experimentally at the single collision level by the group of Prof. C. K. Ni using the crossed molecular beam technique. From their experimental observations, they concluded a 0.3%-1% of energy transfer collisions were supercollisions at three collisions energies, namely 170, 480, and 710 cm-1. Supercollisions give rise to anomalously large amounts of energy transfer. Even though this percentage is low, the effect of supercollisions on properties, such as the reaction rates is large. Therefore, it is of great interest to understand the mechanism of supercollision in this system. In order to appropriately simulate the collision, we constructed the intermolecular potential energy surface (PES) between Kr and Az using results from the MP2/6-31G** calculation. As for the intramolecular interactions governing the energy flow within the Az molecule we used a potential reported in the literature, which reproduce spectroscopical data. From the detailed examination of the calculation results, three kinds of mechanism for the supercollision became apparent: the complex mechanism, the double hit mechanism and the single hit mechanism. In addition, our results show that a complex forming mechanism is as important as the other mechanisms at low collision energies, while at high energies the percentage of supercollisions coming from this mechanism decreases greatly.