Iqbal Azhar, Cheung Michelle S Y, Nix Michael G D, Stavros Vasilios G
Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
J Phys Chem A. 2009 Jul 23;113(29):8157-63. doi: 10.1021/jp9031223.
The prevalence of (1)pi sigma* states in the photochemistry of heteroaromatics is becoming increasingly clear from the recent literature. Photodissociation measurements have shown that following excitation of phenol molecules above the S(1)/S(2) conical intersection, H-atoms are eliminated with two distinct ranges of kinetic energy release. Those with high kinetic energy are attributed to direct dissociation while those with low kinetic energy are traditionally attributed to indirect dissociation or statistical unimolecular decay, both pathways giving electronic ground-state phenoxyl fragments. Using a combination of femtosecond pump/probe spectroscopy and velocity map ion imaging techniques, the time and energy resolved H-atom elimination in phenol-h(6) and phenol-d(5), following excitation at 200 nm has been measured. At the lowest kinetic energies, the H-atom elimination from phenol-d(5) occurs in <150 fs, in sharp contrast to what one expects from a statistical decay process. This implies that these H-atoms are formed through a direct dissociation process yielding electronically excited phenoxyl fragments.
从最近的文献中可以越来越清楚地看到，杂环芳烃光化学中（1）πσ*态的发生率。光解离测量表明，在苯酚分子激发到S(1)/S(2)锥形交叉点以上后，氢原子以两个不同的动能释放范围被消除。那些具有高动能的归因于直接解离，而那些具有低动能的传统上归因于间接解离或统计单分子衰变，这两种途径都产生电子基态苯氧基片段。使用飞秒泵浦/探测光谱和速度映射离子成像技术相结合的方法，测量了在200nm激发后，苯酚-h(6)和苯酚-d(5)中时间和能量分辨的氢原子消除情况。在最低动能下，苯酚-d(5)中的氢原子消除发生在<150飞秒内，这与统计衰变过程的预期形成鲜明对比。这意味着这些氢原子是通过直接解离过程形成的，产生电子激发的苯氧基片段。
