Coulter Philip, Grubb Michael P, Koyama Daisuke, Sazanovich Igor V, Greetham Gregory M, Orr-Ewing Andrew J
School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K.
Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory , Harwell Oxford, Didcot, Oxfordshire, OX11 0QX, U.K.
J Phys Chem A. 2015 Dec 31;119(52):12911-23. doi: 10.1021/acs.jpca.5b10716. Epub 2015 Dec 17.
The fates of CN radicals produced by ultraviolet (UV) photolysis of ICN in various organic solvents have been examined by transient electronic and vibrational absorption spectroscopy (TEAS and TVAS). Near-UV and visible bands in the TEAS measurement enable direct observation of the CN radicals and their complexes with the solvent molecules. Complementary TVAS measurements probe the products of CN-radical reactions. Geminate recombination to form ICN and INC is a minor pathway on the 150 fs -1300 ps time scales of our experiments in the chosen organic solvents; nonetheless, large infrared transition dipole moments permit direct observation of INC that is vibrationally excited in the C≡N stretching mode. The time constants for INC vibrational cooling range from 30 ps in tetrahydrofuran (THF) to 1400 ps in more weakly interacting solvents such as chloroform. The major channel for CN removal in the organic solvents is reaction with solvent molecules, as revealed by depletion of solvent absorption bands and growth of product bands in the TVA spectra. HCN is a reaction product of hydrogen atom abstraction in most of the photoexcited solutions, and forms with vibrational excitation in both the C-H and C≡N stretching modes. The vibrational cooling rate of the C≡N stretch in HCN depends on the solvent, and follows the same trend as the cooling rate of the C≡N stretch in INC. However, in acetonitrile solution an additional reaction pathway produces C3H3N2(•) radicals, which release HCN on a much longer time scale.
通过瞬态电子和振动吸收光谱法（TEAS和TVAS）研究了在各种有机溶剂中ICN经紫外线（UV）光解产生的CN自由基的命运。TEAS测量中的近紫外和可见波段能够直接观察CN自由基及其与溶剂分子的络合物。互补的TVAS测量探测CN自由基反应的产物。在我们所选有机溶剂的150飞秒至1300皮秒时间尺度上，双自由基复合形成ICN和INC是一条次要途径；尽管如此，大的红外跃迁偶极矩使得能够直接观察到在C≡N伸缩模式下振动激发的INC。INC振动冷却的时间常数范围从四氢呋喃（THF）中的30皮秒到氯仿等相互作用较弱的溶剂中的1400皮秒。TVA光谱中溶剂吸收带的耗尽和产物带的增长表明，有机溶剂中CN去除的主要途径是与溶剂分子反应。HCN是大多数光激发溶液中氢原子提取的反应产物，并且在C-H和C≡N伸缩模式下均以振动激发形成。HCN中C≡N伸缩的振动冷却速率取决于溶剂，并且与INC中C≡N伸缩的冷却速率遵循相同的趋势。然而，在乙腈溶液中，另一条反应途径产生C3H3N2(•)自由基，其在长得多的时间尺度上释放HCN。
