特定能態二氯丙烷離子的解離動態學：門檻光電子光離子同現質譜與量子理論計算

Abstract

本論文利用門檻光電子光離子同現質譜技術，研究1,3二氯丙烷和2,2二氯丙烷的光游離解離動態學。我們由1,3二氯丙烷在光能量範圍10.8-12.0 eV的同現質譜得到C3H5Cl+和C3H5+的初現能分別是£ 10.79和11.77 ± 0.03 eV，與形成 c-C3H5Cl+ + HCl和CH2CHCH2+ + HCl + Cl的G3B3預測反應能量10.62和11.77 eV一致。我們也預測1,3二氯丙烷離子( 6, C1 )在形成c-C3H5Cl+ + HCl時，會經過一個五圓環的過渡態，形成五圓環的過渡態無需能障的結果和實驗觀察到釋放的動能近似統計分佈的結果相吻合。相反地，我們由2,2二氯丙烷的同現質譜中並沒有觀測到2,2二氯丙烷離子，而且2,2二氯丙烷離子解離形成CH3CClCH3+ + Cl 釋放出大量的動能，搭配我們使用理論計算2,2二氯丙烷離子解離形成CH3CClCH3+ + Cl 所需的能障10.74 eV (G3B3)比實驗觀測到的游離能10.78 eV低，推測2,2二氯丙烷被光游離後，由於結構不穩定，馬上就碎裂掉Cl並且釋放出大量的動能。 結合同現實驗和G3B3理論計算的結果，我們討論1,3二氯丙烷離子和2,2二氯丙烷離子的解離產物與釋放動能的差異性和可能的解離機制。

The dissociative photoionization of 1,3-C3H6Cl2 and 2,2-C3H6Cl2 were investigated with threshold photoelectron-photoion coincidence (TPEPICO) technique and theoretical calculations. For 1,3-C3H6Cl2, fragment ions C3H5Cl+ and C3H5+ were observed in the coincidence spectra in a region 10.8-12.0 eV; their appearance energies £10.79 and 11.77±0.03 eV agree with the predicted G3B3 reaction energies 10.62 and 11.77 eV for formation of c-C3H5Cl+ + HCl and CH2CHCH2+ + HCl + Cl, respectively. A predicted dissociation mechanism from 1,3-C3H6Cl2+ (6, C1) via a five-membered ring transition state for formation c-C3H5Cl+ + HCl supports an observation of a statistical energy distribution upon dissociation. In contrast, 2,2-C3H6Cl2+ was absent and dissociation of 2,2-C3H6Cl2+ to form CH3CClCH3+ + Cl with substantial releases of kinetic energies was observed. A predicted G3B3 reaction energy 10.74 eV for formation of CH3CClCH3+ + Cl smaller than the ionization energy 10.78 eV for 2,2-C3H6Cl2 and lack of parent ion 2,2-C3H6Cl2+ is probably due to an unstable 2,2-C3H6Cl2+ which dissociates into CH3CClCH3+ + Cl with large kinetic energies released. We discuss the differences in the dissociation products and releases of kinetic energies upon dissociation between 1,3-C3H6Cl2+ and 2,2-C3H6Cl2+ based on experimental results and G3B3 calculations