环戊二烯与氦的碰撞激发：一套完整的速率系数及天体物理应用
Collisional excitation of cyclopentadiene by helium. A complete set of rate coefficients and astrophysical applications
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中文总结 AI 辅助
本研究通过量子散射计算获得环戊二烯与氦碰撞的完整转动激发速率系数，用于辐射传输模拟，为星际复杂有机分子的探测解释提供关键数据支持。
中文摘要 AI 辅助
包括大型环状物种在内的复杂有机分子普遍存在于星际空间，在各种天体化学过程中发挥关键作用。环戊二烯（c-C₅H₆）是一种五元环状烃，最近在TMC-1及其他一些星际分子云中被探测到。虽然已有准确的光谱数据，但迄今为止，其转动跃迁的碰撞速率系数仍处于缺失状态，这可能会限制观测结果的解释。本研究旨在提供一套完整的、针对c-C₅H₆与氦碰撞产生的转动激发的态-态热速率系数，这对天体物理环境中的非局域热力学平衡（non-LTE）辐射传输建模至关重要，同时研究该分子在冷分子云物理条件下离热化的程度。研究采用基于[c-C₅H₆ + He]碰撞复合物的高度相关三维势能面的 close-coupling（CC， close-coupling，密耦合）和 coupled states（CS，耦合态）方法进行准确的量子散射计算，计算覆盖了广泛的转动态（从j=0到j≤25）和动力学温度（从10到50 K）。我们计算了正-C₅H₆和仲-C₅H₆的完整热速率系数集。辐射传输模拟表明，在典型冷云条件下，环戊二烯的大多数转动能级完全热化，仅表现出微小的非局域热力学平衡（non-LTE）效应。不过，本研究首次将准确的态-态速率系数用于已在太空中探测到的大型五元环状物种的辐射传输模拟，这使得我们能够得出一些一般性结论，并为未来复杂天体分子的研究铺平道路，从而能够更精确地解释即将到来的探测结果。
英文摘要
Complex organic molecules, including large cyclic species, are prevalent in interstellar space and play a key role in various astrochemical processes. Cyclopentadiene (c-C5H6) is a five-membered cyclic hydrocarbon recently detected in TMC-1 and some other interstellar molecular clouds. While accurate spectroscopic data were available, collisional rate coefficients for its rotational transitions were missing so far, introducing a potential limitation in the interpretation of the observations. This study aims to provide a comprehensive set of state-to-state thermal rate coefficients for the rotational excitation of c-C5H6 due to collisions with helium, crucial for non-local thermodynamic equilibrium (non-LTE) radiative transfer modelling in astrophysical environments, and to examine how far the molecule is from thermalisation under the physical conditions of cold molecular clouds. The research employed accurate quantum scattering calculations using the close-coupling (CC) and coupled states (CS) methods, based on a highly-correlated three-dimensional potential energy surface for the [c-C5H6 + He] collisional complex. Calculations were performed for a wide range of rotational states (from j = 0 to j \leq 25) and kinetic temperatures (from 10 to 50 K). We calculated a complete set of thermal rate coefficients for both ortho- and para-C5H6. Radiative transfer simulations demonstrated that most rotational levels of cyclopentadiene are fully thermalized under typical cold cloud conditions and exhibit minor non-LTE effects. Nevertheless, this study is the first to utilise accurate state-to-state rate coefficients for radiative transfer simulation of a large, five-membered cyclic species detected in space. This allows to draw some general conclusions and paves the way for future studies of complex astromolecules that will enable a more precise interpretation of upcoming detections.
发表机构
- HUN-REN Institute for Nuclear Research（匈牙利科学院核物理研究所）
- Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251（雷恩大学，法国国家科学研究中心，雷恩物理研究所）
- Instituto de Física Fundamental (IFF-CSIC)（基础物理研究所）
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