Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China.
Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States.
J Phys Chem A. 2023 Jan 12;127(1):195-202. doi: 10.1021/acs.jpca.2c07746. Epub 2022 Dec 27.
While the rigid-rotor (RR) approximation is usually considered to be accurate for describing pure rotationally inelastic scattering involving diatoms in their ground or low-lying vibrational states, its validity in scattering involving polyatomic molecules has not been fully examined. The existence of soft/anharmonic vibrational modes in polyatomic molecules could make rotational-vibrational energy transfer rather efficient, thus undermining the premise of the RR approximation. In this work, we conduct a benchmark test of the RR approximation in the rotationally inelastic scattering of the HO( = 0, 1) + Ar system by comparing with full-dimensional quantum scattering calculations. We demonstrate that the error in the RR rate coefficient for = 0 is less than 5%, while it can reach up to 20% for some initial states within the = 1 manifold. These results indicate that the RR approximation gradually deteriorates with increasing quantum number . Vibrational relaxation dynamics of this system was also studied, and it is found that transitions from initial states with a large rotational quantum number of projection on the principal axis are more efficient. These results shed valuable light on ro-vibrationally inelastic scattering involving polyatomic molecules.
虽然刚性转子 (RR) 近似通常被认为在描述涉及基态或低能振动态的二原子纯旋转非弹性散射时是准确的，但它在涉及多原子分子的散射中的有效性尚未得到充分检验。多原子分子中存在软/非谐振动模式可能使旋转-振动能量转移非常有效，从而破坏 RR 近似的前提。在这项工作中，我们通过与全维量子散射计算进行比较，对 HO( = 0, 1) + Ar 体系的旋转非弹性散射中 RR 近似进行了基准测试。我们证明，对于 = 0，RR 速率系数的误差小于 5%，而对于 = 1 支中的某些初始态，误差可达 20%。这些结果表明，RR 近似随着量子数 的增加而逐渐恶化。还研究了该体系的振动弛豫动力学，发现初始态在主轴上的投影具有较大转动量子数的跃迁更为有效。这些结果为涉及多原子分子的罗振动非弹性散射提供了有价值的信息。
