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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Preferential Solvation in the Collisional Deactivation of Vibrationally Highly Excited Azulene in Supercritical Xenon/Ethane Mixtures
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Preferential Solvation in the Collisional Deactivation of Vibrationally Highly Excited Azulene in Supercritical Xenon/Ethane Mixtures

机译：在超临界氙/乙烷混合物中振动高度激发的偶氮苯的碰撞钝化中的优先溶剂化

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摘要

The collisional deactivation of vibrationally highly excited azulene was studied in equimolar supercritical mixtures of xenon and ethane at 385 K from gas- to liquid-phase densities. Azulene with an energy of ～20 000 cm~(-1) was generated by laser excitation into the S_1 state and subsequent internal conversion to the S_0~* ground state. The loss of vibrational energy was monitored by transient absorption at the red edge of the S_3 ← S_0 absorption band at 290 nm. Transient signals were converted into energy-time profiles using hot band absorption coefficients from shock wave experiments for calibration and accounting for solvent shifts of the spectra. Under all conditions, the energy decays were exponential. At densities below 1 mol/L, the observed collisional deactivation rate constants k_c of the mixture were equal to the sum of the individual contributions of ethane and xenon collisions as expected from simple gas kinetics. At mixture densities above 2 mol/L, k_c is smaller than the deactivation rate constant found in neat ethane at half the density. This behavior can be rationalized by an isolated binary collision (IBC) model which relates the collision frequency Z to the radial distribution function g(r) of an attractive hard-sphere particle in a Lennard-Jones fluid. Radial distribution functions obtained by Monte Carlo simulations clearly show that at high densities the less efficient collider xenon preferentially solvates the azulene molecule, reducing the number of azulene-ethane collisions and, therefore, the overall collisional deactivation rate constant with respect to neat ethane solution.
机译：在385 K的氙和乙烷等摩尔超临界混合物中，从气相密度到液相密度，研究了振动激发的氮z的碰撞失活。通过激光激发进入S_1状态并随后内部转换为S_0〜*基态，生成了能量约为20,000 cm〜（-1）的氮杂。通过在290 nm处S_3←S_0吸收带的红色边缘处的瞬态吸收来监测振动能量的损失。使用来自冲击波实验的热带吸收系数将瞬态信号转换为能量-时间曲线，以进行校准并考虑光谱的溶剂漂移。在所有条件下，能量衰减都是指数级的。在低于1 mol / L的密度下，所观察到的混合物的碰撞失活速率常数k_c等于从简单气体动力学所预期的乙烷和氙气碰撞的个体贡献之和。在高于2 mol / L的混合物密度下，k_c小于纯乙烷在一半密度下的失活速率常数。此行为可以通过孤立的二进制碰撞（IBC）模型来合理化，该模型将碰撞频率Z与Lennard-Jones流体中有吸引力的硬球粒子的径向分布函数g（r）相关联。通过蒙特卡洛模拟获得的径向分布函数清楚地表明，在高密度时，效率较低的对撞机氙气优先溶解了氮z分子，从而减少了氮z-乙烷碰撞的次数，因此降低了相对于纯乙烷溶液的整体碰撞失活速率常数。

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