Vibrational Dynamics of Electronic Excited Molecules

研究了电子激发态乙炔的振动动力学和反应动力学。乙炔在电子激发态A^^ ~中的振动能级结构被认为是2^n3^m振动态的递进。然而，本文证明了V_3‘模与v_4’/v_6'模非谐耦合，形成由2^m3^n， 2^m3^<n-1>(4/5)^2, 2^m3^<n-2>(4/6)^4, ..........组成的多面体结构用红外-紫外双共振光谱研究了非均匀振动态，发现了相同类型的非调和耦合。在这种情况下，具有奇数量子数的（4/6）状态与3^n状态耦合。通过对谱线宽度的观察，确定了乙炔在A^^ ~态各振动能级上的预解离速率常数。发现速率常数与振动宇称级数或级数无关。这可以归因于V_3‘和V_4’/V_6'模态之间的非谐波耦合，这使得梯度态和非梯度态具有相似的振动特性。发现激发态介导的乙炔向C_2H(X^^)+H的预解在激发能51100 cm^<-1>附近停止，远超过A态的绝热解离阈值。在这个能量下，乙炔仍以大约10^<10> s^<-1>的速率预解生成C_2H(a ^^ ~) + H.4。提出了一种新的实验技术——差温激光诱导荧光光谱技术，该技术能够分离LIF光谱中重叠的冷热带。

Vibrational and reaction dynamics of electronic excited acetylene have been investigated.1. The vibrational level structure of acetylene in the electronic excited A^^〜 state was believed to be the progressions of the 2^n3^m vibrational states. However, in this work it was proved that the V_3' mode couples anharmonically with the ungerade v_4'/v_6' mode to form a polyad structure composed of the 2^m3^n, 2^m3^<n-1>(4/5)^2, 2^m3^<n-2>(4/6)^4, ………. The same type of the anharmonic coupling was found for the ungerade vibrational states which were investigated by an IR-UV double resonance spectroscopy. In this case, the (4/6) states having odd quantum numbers couple with the 3^n state.2. The predissociation rate constants of acetylene in respective rovibronic levels of the A^^〜 state were determined through observation of the spectral line-widths. The rate constants were found to be independent of the vibrational parity gerade or ungerade. This can be attributed to the anharmonic coupliig between the V_3' and V_4'/V_6' modes which causes the gerade and ungerade states to have a similar vibrational chracteristics.3. It was found that the triplet state-mediated predissociation of excited acetylene toward C_2H(X^^〜)+H ceases around the excitation energy of 51100 cm^<-1> which is far beyond the adiabatic dissociation threshold of the A state. At this energy, acetylene still predissociates at a rate of around 10^<10> s^<-1> to form C_2H(A^^〜) + H.4. A new experimental technique, Differential Temperature Laser Induced Fluorescence Spectroscopy, was developed which is capable of separating overlapping cold and hot bands of a LIF spectrum.