Montero S, Thibault F, Tejeda G, Fernández J M
Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain.
J Chem Phys. 2006 Sep 28;125(12):124301. doi: 10.1063/1.2353121.
Inelastic collisions in natural H2 are studied from the experimental and theoretical points of view between 10 and 140 K. Rotational populations and number densities measured by Raman spectroscopy along supersonic expansions of H2 provide the link between experimental and theoretical rotranslational state-to-state rate coefficients of H2 in the vibrational ground state. These rates are calculated in the close-scattering approach with the MOLSCAT code employing a recent ab initio H2-H2 potential. The calculated rates are assessed by means of a master equation describing the time evolution of the experimental rotational populations. The feasibility for obtaining the rates on the sole basis of the experiment is discussed. The dominant processes j(1)j(2)-->j'(1)j'(2) in the investigated thermal range are found to be 21-->01 >30-->12 >31-->11, proving the importance of double processes such as 30-->12. Good agreement is found between theory and experiment, as well as with earlier ultrasonic measurements of relaxation times. A spectral representation is proposed in order to visualize quantitatively the collisional contributions in any nonequilibrium time evolving process.
从实验和理论角度研究了10至140K温度范围内天然氢气中的非弹性碰撞。通过拉曼光谱沿氢气超声膨胀测量的转动布居和数密度，建立了基振动态下氢气实验和理论转动平动态对态速率系数之间的联系。这些速率是在紧密散射近似下，使用MOLSCAT程序并采用最新的从头算氢气-氢气势能计算得到的。通过描述实验转动布居时间演化的主方程对计算得到的速率进行评估。讨论了仅基于实验获得速率的可行性。发现在研究的热范围内，主要过程j(1)j(2)-->j'(1)j'(2)为21-->01 >30-->12 >31-->11，证明了如30-->12这样的双过程的重要性。理论与实验之间以及与早期超声弛豫时间测量结果之间均取得了良好的一致性。为了定量可视化任何非平衡时间演化过程中的碰撞贡献，提出了一种光谱表示方法。
