Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
J Am Chem Soc. 2011 Mar 30;133(12):4164-7. doi: 10.1021/ja108598w. Epub 2011 Mar 3.
Ultrafast time-resolved mass spectrometry and structural dynamics experiments on trans-stilbene, cis-stilbene, and azobenzene, with excitation to high-lying electronic states, reveal a rich diversity of photochemical reaction dynamics. All processes are found to be quite unlike the well-known photochemistry on lower electronic surfaces. While in trans-stilbene, excitation at 6 eV induces a phenyl twisting motion, in cis-stilbene it leads to an ultrafast ring-closing to form 4a,4b-dihydrophenanthrene. Azobenzene dissociates on an ultrafast time scale, rather than isomerizing as it does on a lower surface. The photochemical dynamics of the sample molecules proceed along steep potential energy surfaces and conical intersections. Because of that, the dynamics are much faster than vibrational relaxation, the randomizing effects from vibrational energy scrambling are avoided, and excitation-energy specific reaction dynamics results.
对反式二苯乙烯、顺式二苯乙烯和偶氮苯的超快时间分辨质谱和结构动力学实验，用高电子态激发，揭示了丰富多样的光化学反应动力学。所有过程都与熟知的低电子表面的光化学完全不同。在反式二苯乙烯中，在 6eV 的激发下诱导苯环扭转运动，而在顺式二苯乙烯中则导致超快的环闭合形成 4a，4b-二氢菲。偶氮苯在超快时间尺度上解离，而不是像在低表面上那样异构化。样品分子的光化学反应动力学沿着陡峭的势能面和锥形交叉进行。因此，动力学比振动弛豫快得多，避免了振动能量混合的随机效应，产生了激发能特定的反应动力学结果。
