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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Rotational and Vibrational Relaxation of Methane Excited to 2nu_3 in CH_4/H_2 and CH_4/He Mixtures at 296 and 193 K from Double-Resonance Measurements
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Rotational and Vibrational Relaxation of Methane Excited to 2nu_3 in CH_4/H_2 and CH_4/He Mixtures at 296 and 193 K from Double-Resonance Measurements

机译：通过双共振测量，在296和193 K的CH_4 / H_2和CH_4 / He混合物中激发到2nu_3的甲烷的旋转和振动弛豫

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A series of time-resolved IR-IR double-resonance experiments have been conducted where methane molecules are excited into a selected rovibrational level of the 2nu_3(F_2)vibrational substate of the tetradecad and where the time evolution of the population of the various energy levels is probed by a tunable continuous wave laser.The rotational relaxation and vibrational energy transfer processes occurring in methane upon inelastic CH_4-H_2 and CH_4-He collisions have been investigated by this technique at room temperature and at 193 K.By probing transitions in which either the lower or the upper level is the laser-excited level,rotational depopulation rates in the 2nu_3(F_2)substate were measured.The rate constants for CH_4-H_2 collisions were found to be 17.7 +-2.0 and 18.9 +-2.0 mus~(-1)Torr~(-1)at 296 and 193 K,respectively,and for CH_4-He collisions they are 12.1 +-1.5 and 16.0 +-2.0 mus~(-1)Torr~(-1)at the same temperatures.The vibrational relaxation was investigated by probing other stretching transitions such as 2nu_3(F_2)-nu_3,nu_3 + 2nu_4-2nu_4,and nu_3 + nu_4-nu_4.A kinetic model,taking into account the main collisional processes connecting energy levels up to 6000 cm~(-1),that has been developed to describe the various relaxation pathways allowed us to calculate the temporal evolution of populations in these levels and to simulate double-resonance signals.The different rate coefficients of the vibrational relaxation processes involved in these mixtures were determined by fitting simulated signals to the observed signals corresponding to assigned transitions.For vibration to translation energy transfer processes,hydrogen is a much more efficient collision partner than helium,nitrogen,or methane itself at 193 K as well as at room temperature.
机译：已经进行了一系列时间分辨的IR-IR双共振实验，其中甲烷分子被激发到四十年的2nu_3（F_2）振动子状态的选定振动水平，并且各个能级的人口随时间变化这项技术已在室温和193 K下研究了在无弹性CH_4-H_2和CH_4-He碰撞时甲烷中发生的旋转弛豫和振动能量转移过程。较低或较高水平是激光激发水平，测量了2nu_3（F_2）亚态的旋转种群减少率。CH_4-H_2碰撞的速率常数为17.7 + -2.0和18.9 + -2.0 mus〜（ -1）Torr〜（-1）分别在296和193 K下发生，对于CH_4-He碰撞，在相同温度下它们分别为12.1 + -1.5和16.0 + -2.0 mus〜（-1）Torr〜（-1）振动松弛通过探测诸如2nu_3（F_2）-nu_3，nu_3 + 2nu_4-2nu_4和nu_3 + nu_4-nu_4的拉伸过渡。一个动力学模型，考虑到连接能量级高达6000 cm〜（-1）的主要碰撞过程，因此已经开发了描述各种弛豫途径的方法，这些途径使我们能够计算这些水平上的种群的时间演化并模拟双共振信号。通过将模拟信号拟合到这些混合物来确定这些混合物所涉及的振动弛豫过程的不同速率系数。观察到的信号对应于指定的跃迁。对于振动到平移能量传递过程，在193 K和室温下，氢比氦，氮或甲烷本身的碰撞伙伴效率更高。

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