Institut UTINAM UMR CNRS 6213, Université de Franche-Comté, 16 Route de Gray, 25030 Besançon cedex, France.
Phys Chem Chem Phys. 2011 Dec 7;13(45):20326-34. doi: 10.1039/c1cp22232e. Epub 2011 Oct 13.
The case of symmetric tops CH(3)X (X = Br, Cl, F, …) perturbed by non-polar diatoms Y(2) (Y = N(2), O(2), …) is analysed from the viewpoint of theoretical collisional broadening of their rotational lines observed in atmospheric spectra. A semi-classical approach involving an exponential representation of the scattering operator and exact trajectories governed by the isotropic potential is presented. For the first time the active molecule is strictly treated as a symmetric top and the atom-atom interactions are included in the intermolecular potential model. It is shown for the CH(3)Cl-O(2) system that these interactions contribute significantly to the line width for all values of the rotational quantum numbers J and K. Additional testing of modifications required in the semi-classical formalism for a correct application of the cumulant expansion is performed and it is shown that the use of the cumulant average on the rotational states of the perturbing molecule leads to entirely negligible effects for the not very strongly interacting CH(3)Cl-O(2) system. In order to check the theoretical predictions and to extend the scarce experimental data available in the literature to higher values of the rotational quantum numbers, new measurements of room-temperature O(2)-broadened CH(3)Cl rotational lines are carried out by a photomixing continuous-wave terahertz spectrometer. The experimental line widths extracted with a Voigt profile model demonstrate an excellent agreement with theoretical results up to very high J-values (J = 31, 37, 40, 45, 50).
对称顶 CH(3)X (X = Br, Cl, F, …) 被非极性双原子 Y(2) (Y = N(2), O(2), …) 微扰的情况，从理论上分析了大气光谱中观察到的其转动线的碰撞展宽。提出了一种半经典方法，其中包括散射算子的指数表示和由各向同性势能控制的精确轨迹。首次将活性分子严格视为对称顶，并将原子-原子相互作用纳入分子间势能模型。对于 CH(3)Cl-O(2)系统，研究表明这些相互作用对所有转动量子数 J 和 K 的线宽都有显著贡献。对半经典形式主义中为正确应用累积展开所需的修改进行了额外的测试，并表明在扰动分子的转动态上使用累积平均值会导致对相互作用不强的 CH(3)Cl-O(2)系统产生完全可以忽略的影响。为了检验理论预测并将文献中有限的实验数据扩展到更高的转动量子数，使用光电混合连续波太赫兹光谱仪进行了室温 O(2)展宽 CH(3)Cl 转动线的新测量。用 Voigt 轮廓模型提取的实验线宽与理论结果非常吻合，直到非常高的 J 值 (J = 31, 37, 40, 45, 50)。
