Chahal Pooja, Dhilip Kumar T J
Quantum Dynamics Lab, Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar 140001, India.
J Chem Phys. 2025 Sep 14;163(10). doi: 10.1063/5.0284377.
The interstellar medium (ISM) is a complex and dynamic environment in which molecular collisions play a crucial role. Among these, protonated carbon chains are of great interest due to the presence of a permanent dipole moment and their relevance in describing astrochemical processes, making their detection possible in cold molecular clouds such as TMC-1. C5H+ (1Σg+) is an important molecule for understanding the formation and evolution of carbon-rich environments. However, to accurately model its abundance and spectroscopic properties, it is essential to account for its collisional interactions with H2, the most abundant molecule in the ISM. In this study, we present a quantum dynamical study for the C5H+-H2 collision, employing high-level CCSD(T)-F12a/aug-cc-pVTZ calculations to construct an accurate potential energy surface (PES). The PES is further augmented using a neural network fitting model, ensuring spectroscopic accuracy. The PES is expanded into radial components using bispherical harmonics. Then, close coupling methods were used to calculate cross sections and rate coefficients for different rotational transitions of C5H+, up to 100 K. Throughout the temperature range, a propensity is observed for even transitions over odd transitions. The rate coefficients for He and H2 collisions are compared for C5H+, C5, and C6H-. For both low and high temperatures, rate coefficients for C5H+ are found to be higher than C5 and C6H- for both the He and H2 collisions.
星际介质（ISM）是一个复杂且动态的环境，其中分子碰撞起着至关重要的作用。在这些碰撞中，质子化碳链因其永久偶极矩的存在以及在描述天体化学过程中的相关性而备受关注，这使得它们能够在诸如TMC - 1这样的冷分子云中被探测到。C5H +（1Σg +）是理解富碳环境形成和演化的重要分子。然而，为了准确模拟其丰度和光谱性质，考虑其与ISM中最丰富的分子H2的碰撞相互作用至关重要。在本研究中，我们对C5H + - H2碰撞进行了量子动力学研究，采用高水平的CCSD(T)-F12a/aug-cc-pVTZ计算来构建精确的势能面（PES）。通过神经网络拟合模型进一步增强PES，以确保光谱精度。使用双球谐函数将PES扩展为径向分量。然后，使用密耦方法计算C5H +不同转动跃迁的截面和速率系数，温度高达100 K。在整个温度范围内，观察到偶数跃迁比奇数跃迁更具倾向性。比较了C5H +、C5和C6H -与He和H2碰撞的速率系数。对于低温和高温，发现C5H +与He和H2碰撞的速率系数均高于C5和C6H -。
