Reichardt Christian, Schroeder Jörg, Schwarzer Dirk
Abteilung Spektroskopie und Photochemische Kinetik, Max-Planck-Institut für Biophysikalische Chemie, 37070 Göttingen, Germany.
J Phys Chem A. 2007 Oct 11;111(40):10111-8. doi: 10.1021/jp0742968. Epub 2007 Sep 15.
The ultrafast photofragmentation of arylperoxycarbonates R-O-C(O)O-O-tert-butyl (R = naphthyl, phenyl) is studied using femtosecond UV excitation at 266 nm and mid-infrared broadband probe pulses to elucidate the dissociation mechanism. Our experiments show that the rate of fragmentation is determined by the S1-lifetime of the peroxide, i.e., the time constants of S1 decay and of CO2 and R-O* formation are identical. The fragmentation times are solvent dependent and for tert-butyl-2-naphthylperoxycarbonate (TBNC) vary from 25 ps in CH2Cl2 to 52 ps in n-heptane. In the case of the tert-butylphenylperoxycarbonate (TBPC) the decomposition takes 5.5 ps in CD2Cl2 and 12 ps in n-heptane. The CO2 fragment is formed vibrationally hot with an excess energy of about 5000 cm(-1). The hot CO2 spectra at high energy can be modeled assuming Boltzmann distributions with initial vibrational temperatures of ca. 2500 K which relax to ambient temperature with time constants of 280 ps in CCl4 and 130 ps in n-heptane. In CCl4 the relaxed spectra at 1.5 ns show 3.5% residual excitation in the n = 1 level of the asymmetric stretch vibration.
使用266 nm的飞秒紫外激发和中红外宽带探测脉冲研究了芳基过氧碳酸酯R - O - C(O)O - O -叔丁基（R =萘基、苯基）的超快光解离，以阐明其解离机制。我们的实验表明，碎片化速率由过氧化物的S1寿命决定，即S1衰减以及CO2和R - O*形成的时间常数相同。碎片化时间取决于溶剂，对于叔丁基 - 2 -萘基过氧碳酸酯（TBNC），在二氯甲烷中为25 ps，在正庚烷中为52 ps。对于叔丁基苯基过氧碳酸酯（TBPC），在二氯甲烷 - d2中分解需要5.5 ps，在正庚烷中需要12 ps。CO2碎片以约5000 cm⁻¹的过剩能量振动激发形成。高能下的热CO2光谱可以假设为玻尔兹曼分布来建模，初始振动温度约为2500 K，在四氯化碳中以280 ps的时间常数弛豫到环境温度，在正庚烷中以130 ps的时间常数弛豫。在四氯化碳中，1.5 ns时的弛豫光谱在不对称伸缩振动的n = 1能级显示3.5%的残余激发。
