高振動激發態分子之能量轉移

Energy Transfer of Highly Vibrationally Excited Molecules

許旭辰(Hsu-Chen Hsu)

指導教授 ： 林聖賢

共同指導教授 ： 倪其焜

國立臺灣大學/理學院/化學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.02606

摘要

高振動激發態分子的能量轉移在許多的化學過程中，扮演很重要的角色，所以過去不管是實驗或是理論計算方面均有許多的研究。本實驗利用交叉分子束(crossed-beam)配合時間切片速度相配離子影像(time-sliced velocity map ion imaging)偵測技術，藉由(naphthalene)及2-甲基(2-methylnaphthalnene)與氪(Kr)原子的能量轉移，以探討甲基化效應對能量轉移機制的影嚮。經由比較naphthalene與2-methylnaphthalene的實驗結果可以發現不管在碰撞截面積或是能量轉移機率分佈，均無明顯的不同之處。naphthalene及2-methylnaphthalene與氪分子碰撞之碰撞截面積的比例為 σ(naphthalene): σ(2-methylnaphthalene) = 1.08 ± 0.05:1，而能量轉移機率分佈可看出，naphthalene分子轉移移動能到內能上(ΔE_u< 300 cm^(-1))的機率比較多一點，而2-methylnaphthalene有較多的機率轉移振動能到移動能上(-800 cm^(-1) < ΔE_d < -100 cm^(-1))，但是這些差異太小，很接近我們實驗上的誤差。另外，實驗結果也顯示二個分子對超級碰撞的影嚮並沒有明顯的不同。雖然我們的實驗與文獻有所不同，但是我們也不能排除甲基化效應對能量轉移機制的影嚮，過去的研究主要是比較小的分子(如苯及甲基苯)，而我們探討的分子相形之下較大，可能會使得甲基化效應的影嚮不明顯。另外有可能因第一次碰撞後，有部分能量由移動能或是振動能轉移到naphthalene及2-methylnaphthalene的轉動能上，接著第二次或是之後的碰撞由於naphthalene及2-methylnaphthalene的轉動能不同而會造成能量轉移的不同。另一個原因可能是因為我們的實驗是在很低的起始轉動溫度，但是過去的實驗方法是在室溫下進行的，所以對甲基化效應的影嚮也會有不同的結果。

關鍵字

能量轉移 ； 2甲基 ； 甲基化效應 ； 交叉分子束 ； 離子影像

並列摘要

The energy transfer of highly vibrationally excited molecules plays an important role in many chemical processes. A number of experimental and theoretical works have focused on the energy transfer dynamics of highly vibrationally excited molecules. In this thesis, the methylation effects in the energy transfer between Kr atoms and highly vibrationally excited 2-methylnaphthalene in the triplet state were investigated using crossed-beam/time-sliced velocity-map ion imaging technique at a translational collision energy of ~520 cm-1. Comparison of the energy transfer between naphthalene and 2-methylnaphthalene shows that the difference in total collisional cross sections and the difference in energy transfer probability density functions are small. The ratio of the total cross sections is σ(naphthalene): σ(2-methylnaphthalene) = 1.08 ± 0.05:1. The energy transfer probability density function shows that naphthalene has a little larger probability at small T → V/R energy transfer, ΔE_u< 300 cm^(-1), and 2-methylnaphthalene has a little large probability at large V → T energy transfer, -800 cm^(-1) < ΔE_d < -100 cm^(-1). However, these differences are close to our experimental uncertainty. No significant difference in the probability of very large energy transfer, such as supercollisions defined arbitrarily as ΔE_d < -1500 cm^(-1), was observed. No obvious methylation effect observed in this work may be due to the larger size of molecules we used than that (benzene and toluene) in the previous studies. That reduces the influence of the methylation effects in our experiments. The other possibility is that methylation effects may be due to the subsequent successive collisions or internal rotation at room temperature. The energy transfer may result in large difference due to the rotational effects.

並列關鍵字

collision energy transfer ； naphthalene ； 2-methylnaphthalene ； methylation effects ； crossed-molecular beam ； velocity map ion imaging

參考文獻

1. F. A. Lindemann, Trans. Faraday Soc., 17, 598 (1922).

3. I. Oref and D. C. Tardy, Chem. Rev., 90, 1407 (1990).

11. T. Ichimura and Y. Mori, J. Chem. Phys., 83, 117 (1985).

13. A. Pashutski and I. Oref, J. Phys. Chem., 92, 178 (1988).

14. S. Hassoon, I. Oref and C Steel, J Chem. Phys., 89, 1743 (1988).