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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Collisional relaxation of the three vibrationally excited difluorobenzene isomers by collisions with CO2: Effect of donor vibrational mode
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Collisional relaxation of the three vibrationally excited difluorobenzene isomers by collisions with CO2: Effect of donor vibrational mode

机译：与CO2碰撞引起的三个振动激发的二氟苯异构体的碰撞弛豫：供体振动模式的影响

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摘要

Relaxation of highly vibrationally excited 1,2-, 1,3-, and 1,4-difluorobenzne (DFB) by collisions with carbon dioxide has been investigated using diode laser transient absorption spectroscopy. Vibrationally hot DFB (E';approximate to 41 000 cm(-1)) was prepared by 248 nm excimer laser excitation followed by rapid radiationless relaxation to the ground electronic state. Collisions between hot DFB isomers and CO2 result in large amounts of rotational and translational energy transfer from the hot donors to the bath. The CO2 nascent rotational population distribution of the high-J (J = 58-80) tail of the 0000 state was probed at short times following the excimer laser pulse to measure rate constants and probabilities for collisions populating these states. The amount of translational energy gained by CO2 during collisions was determined using Doppler spectroscopy to measure the width of the absorption line for each transition. The energy transfer probability distribution function, P(E,E'), for the large AE tail was obtained by resorting the state-indexed energy transfer probabilities as a function of Delta E. P(E,E') was fit to a biexponential function to determine the average energy transferred in a single DFB/CO2 collision and fit parameters describing the shape of P(E,E). P(E,E) fit parameters for DFB/CO2 and the previously studied C6F6/CO2 system are compared to various donor molecular properties. A model based on Fermi's Golden Rule indicates that the shape of P(E,E') is primarily determined by the low-frequency out-of-plane donor vibrational modes. A fractional mode population analysis is performed, which suggests that for energy transfer from DFB and C6F6 to CO? the two key donor vibrational modes from which energy leaks out of the donor into the bath are nu(11) and nu(16). These "gateway" modes are some of the same modes determined to be the most efficient energy transfer modes by quantum scattering studies of benzene/He collisions.
机译：使用二极管激光瞬态吸收光谱研究了通过与二氧化碳的碰撞来放松高振动激发的1,2-，1,3-和1,4-二氟苯（DFB）。通过248 nm受激准分子激光激发，然后快速无辐射弛豫到基态电子状态，制备了振动热的DFB（E';约41 000 cm（-1））。热的DFB异构体与CO2之间的碰撞会导致大量的旋转和平移能量从热供体传递到熔池。在准分子激光脉冲后的短时间内探测了0000状态的高J（J = 58-80）尾部的CO2新生旋转种群分布，以测量速率常数和碰撞这些状态的概率。使用多普勒光谱仪测定碰撞过程中二氧化碳在碰撞过程中获得的平移能量，以测量每个跃迁的吸收线宽度。通过将状态索引的能量转移概率作为Delta E的函数来获得大AE尾部的能量转移概率分布函数P（E，E'）。P（E，E'）拟合为双指数函数确定一次DFB / CO2碰撞中传递的平均能量，并拟合描述P（E，E）形状的参数。将DFB / CO2和先前研究的C6F6 / CO2系统的P（E，E）拟合参数与各种供体分子特性进行比较。基于费米黄金定律的模型表明，P（E，E'）的形状主要由低频平面外供体振动模式决定。进行了分数模式总体分析，这表明从DFB和C6F6到CO？的能量转移。能量从供体泄漏到熔池中的两个主要供体振动模式是nu（11）和nu（16）。这些“网关”模式是通过苯/ He碰撞的量子散射研究确定为最有效的能量传输模式的某些相同模式。

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