[论文解读] Thermal Desorption of Interstellar Ices:A Review on the Controlling Parameters and Their Implications from Snowlines to Chemical Complexity

Marco Minissale, Yuri Aikawa+17 more|arXiv (Cornell University)|Jan 1, 2022

Astrophysics and Star Formation Studies参考文献 301被引用 113

一句话总结

对星际冰热脱附参数（结合能 Eb 与前指数因子 nu）的全面综述，整合实验与理论方法，并概述雪线与星体形成环境中的化学复杂性影响。

ABSTRACT

The evolution of star-forming regions and their thermal balance are strongly influenced by their chemical composition, which, in turn, is determined by the physicochemical processes that govern the transition between the gas phase and the solid state, specifically icy dust grains (e.g., particle adsorption and desorption). Gas–grain and grain–gas transitions as well as formation and sublimation of interstellar ices are thus essential elements of understanding astrophysical observations of cold environments (e.g., prestellar cores) where unexpected amounts of a large variety of chemical species have been observed in the gas phase. Adsorbed atoms and molecules also undergo chemical reactions that are not efficient in the gas phase. Therefore, the parametrization of the physical properties of atoms and molecules interacting with dust grain particles is clearly a key aspect to interpret astronomical observations and to build realistic and predictive astrochemical models. In this consensus evaluation, we focus on parameters controlling the thermal desorption of ices and how these determine pathways toward molecular complexity and define the location of snowlines, which ultimately influence the planet formation process. We review different crucial aspects of desorption parameters both from a theoretical and experimental points of view. We critically assess the desorption parameters (the binding energies, Eb, and the pre-exponential factor, ?) commonly used in the astrochemical community for astrophysically relevant species and provide tables with recommended values. The aim of these tables is to provide a coherent set of critically assessed desorption parameters for common use in future work. In addition, we show that a nontrivial determination of the pre-exponential factor ? using transition state theory can affect the binding energy value. The primary focus is on pure ices, but we also discuss the desorption behavior of mixed, that is, astronomically more realistic, ices. This allows discussion of segregation effects. Finally, we conclude this work by discussing the limitations of theoretical and experimental approaches currently used to determine the desorption properties with suggestions for future improvements.

研究动机与目标

• 澄清结合能 Eb 与前指数因子 nu 如何支配星际冰的热脱附。
• 调查用于确定热脱附参数 Eb 和 nu 的实验与理论方法，适用于天体化学相关物种。
• 评估脱附参数如何影响气-冰分配、雪线及在恵星形成区域和行星盘中的后续化学反应。
• 提供经批判性评估的 Eb 与 nu 数值并讨论测量和计算中的局限性及未来改进。

提出的方法

• 界定热脱附的控制参数并阐明它们的天体物理含义。
• 综述实验方法（如温度程序性脱附，TPD）并推导 Eb 与 nu 的获得方式。
• 描述 Eb 与 nu 的计算方法，包括表面位点分布以及零级/一级脱附。
• 比较单层与多层脱附机制并相应地解释 TPD 数据。
• 提供将脱附参数整合到天体化学模型与雪线预测中的框架。

实验结果

研究问题

• RQ1 关键的脱附参数 Eb 与前指数因子 nu 是什么？
• RQ2 实验与理论方法如何确定 Eb 与 nu，以及不确定性与局限性？
• RQ3 Eb 与 nu（及其依赖性）如何影响雪线及星形成区和原行星盘中的气-冰平衡？
• RQ4 冰的组成（纯冰与混合冰）及表面效应对脱附行为和天体化学建模有什么影响？

主要发现

• 结合能 Eb 与前指数因子 nu 在很大程度上决定热脱附速率，因此决定冰成分的升华温度。
• 通过过渡态理论对 nu 的非平凡确定会影响推断的 Eb 值，从而影响预测的雪线。
• 本综述为常见星际物种提供经批判性评估的 Eb 与 nu 值，并讨论它们对纯冰及混合冰的适用性。
• 脱附机制（零级 vs 一级）取决于多层与单层覆盖，对 TPD 数据的解释有影响。
• 冰的升华前缘（雪线）对 Eb 与表面组成敏感，影响行星形成情景和盘的化学演化。