A fluorescence lifetime and integral equation study of the quenching of naphthalene fluorescence by bromoethane in super- and subcritical ethane
A fluorescence lifetime and integral equation study of the quenching of naphthalene fluorescence by bromoethane in super- and subcritical ethane
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DOI：
10.1021/ie000057u
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发表时间：
2000-08-01
影响因子：
4.2
通讯作者：
Brennecke, JF
中科院分区：
文献类型：
--
作者：
Roek, DP;Chateauneuf, JE;Brennecke, JF
本文研究了溶剂对超临界和亚临界乙烷中动力学控制的能量转移反应的影响。所选择的反应，萘的荧光猝灭C2 H5 Br，发生远低于扩散控制的限制，在液体溶剂和乙烷。反应。在宽范围的压力下，在40 ℃下从34.8巴延伸到111.6巴，在乙烷中进行了研究，这对应于在0.27和1.76之间的折合密度（rho（r）= rho/rho（c），其中rho（c）是乙烷的临界密度）。超临界和亚临界乙烷的速率常数范围为2.42 × 10（8）至1.36 × 10（9）M-1 s（-1），比扩散控制极限低几个数量级（在这些条件下约为10（11）M-1 s（-1））。如在几个以前的报告中，表观速率常数，基于反应物的本体浓度，在超临界区域中随着压力的降低而急剧增加。更重要的是，在降低的密度低于约0.44时，基于体相浓度的表观速率常数随压力降低而降低。由于速率常数在各种液体溶剂中对溶剂不敏感，我们将乙烷中的表观速率常数的行为归因于萘周围C2 H5 Br的局部组合物增强。此外，我们提出了令人信服的理论（积分方程计算的基础上）的结果，确认最大的局部组成的C2 H5 Br萘附近的密度降低0.44。这是第一次在如此广泛的密度范围内进行简单的双分子反应的实验研究。此外，它是第一个表现出最大的反应速率，这对应于预期的最大的局部组成增强。
We report on the solvent effect on a kinetic-controlled energy-transfer reaction in super- and subcritical ethane. The reaction chosen, the quenching of naphthalene fluorescence by C2H5Br, occurs well below the diffusion-controlled limit in liquid solvents and in ethane. The reaction. was studied in ethane over a wide range of pressures, extending from 34.8 to 111.6 bar at 40 degrees C, which corresponds to reduced densities (rho(r) = rho/rho(c), where rho(c) is the critical density of ethane) between 0.27 and 1.76. The rate constants in super- and subcritical ethane range from 2.42 x 10(8) to 1.36 x 10(9) M-1 s(-1), which is several orders of magnitude below the diffusion-controlled limit (which is on the order of 10(11) M-1 s(-1) at these conditions). As in several previous reports, the apparent rate constants, based on bulk concentrations of the reactants, increase dramatically with decreasing pressure in the supercritical region. More importantly, at reduced densities below about 0.44, the apparent rate constants based on bulk concentrations decrease with decreasing pressure. Because the rate constants are solvent insensitive in a variety of liquid solvents, we attribute the behavior of the apparent rate constants in ethane to local composition enhancement of C2H5Br around naphthalene. In addition, we present compelling theoretical (based on integral equation calculation) results that confirm a maximum in the local composition of C2H5Br around naphthalene near a reduced density of 0.44. This is the first experimental study of a simple, bimolecular reaction over such a wide range of densities. Moreover, it is the first to show a maximum in the reaction rate, which corresponds to the expected maximum in the local composition enhancement.