激發態鈣原子(31D)與甲烷分子之氣體反應動力學研究

Abstract

經由激發-偵測技術搭配位能面計算(PES)，可以得到Ca(4s3d1D)+CH4 → CaH (X2Σ+)+CH3反應的初生態產物CaH之轉動振動光譜。藉由轉動振動光譜，可以進一步推測得知初生態CaH的轉動分佈，並可推得波茲曼轉動分佈溫度在振動態v=0及v=1時分別為1012±102K及834±70K。且可得知初生態CaH在不同的振動態v=0及v=1的分佈比例是CaH(v=0)/CaH(v=1)=3.97±0.26，其所對應到的波玆曼振動溫度為1313±173K。並可藉由轉動振動光譜推測得知產物初生態CaH之轉動及振動的能量分別是461±40cm-1及253.5cm-1。藉由壓力效應實驗，時間差效應實驗及能量效應實驗可以驗證反應產物CaH為初生態狀態，並非經由轉動冷卻或多次碰撞而得到的產物。在溫度效應實驗中，可以藉由阿瑞尼士方程式做佈居與溫度的倒數的關係圖，依據所得斜率可以求得此反應之反應能為2695±210cm-1，意即表示此反應進行為一吸熱反應。搭配位能面理論計算，可以進一步推知反應機制主要是採插入式。Ca(31D)以C2v或Cs對稱接近CH4。

The reaction pathway for Ca(4s3d1D)+CH4→CaH(X2Σ+)+CH3 has been investigated by using the pump–probe technique in combination with potential energy surface (PES) calculations. The nascent product distributions of CaH have been found with a Boltzmann rotational temperature of 1012±102 K and 834± 70K for the v=0 and 1 levels, respectively, and summations of the (v’,v”)=(0,0) and (v’,v”)=(1,1) rovibrational intensities separately show that the population ratio of CaH(v=0)/CaH(v=1) yields a value of 3.97+0.26, which corresponding to a Boltzmann vibrational temperature of 1313±173 K. The rotational and vibrational energy partitions in CaH have been estimated to be 461±40cm-1and 253.5cm-1, respectively. The rotational distributions were obtained to be in the nascent states, free from interference of rotational cooling and secondary reaction processes by several dependences. The Arrhenius plot of the rotational intensity versus the reciprocal of temperature yields an activation energy, 2695+210cm-1, indicating that the reactive collision process should be an endothermic reaction. According to the PES calculations, the pathway is found to favor an insertion mechanism. Ca(31D) approaches CH4 in C2v or Cs symmetry.