{"title":"将结合能分布纳入气冰天体化学模型的框架","authors":"Kenji Furuya","doi":"arxiv-2408.02958","DOIUrl":null,"url":null,"abstract":"One of the most serious limitations of current astrochemical models with the\nrate equation (RE) approach is that only a single type of binding site is\nconsidered in grain surface chemistry, although laboratory and quantum chemical\nstudies have found that surfaces contain various binding sites with different\npotential energy depths. When various sites exist, adsorbed species can be\ntrapped in deep potential sites, increasing the resident time on the surface.\nOn the other hand, adsorbed species can be populated in shallow sites,\nactivating thermal hopping and thus two-body reactions even at low\ntemperatures, where the thermal hopping from deeper sites is not activated.\nSuch behavior cannot be described by the conventional RE approach. In this\nwork, I present a framework for incorporating various binding sites (i.e.,\nbinding energy distribution) in gas-ice astrochemical models as an extension of\nthe conventional RE approach. I propose a simple method to estimate the\nprobability density function for the occupation of various sites by adsorbed\nspecies, assuming a quasi-steady state. By using thermal desorption and hopping\nrates weighted by the probability density functions, the effect of binding\nenergy distribution is incorporated into the RE approach without increasing the\nnumber of ordinary differential equations to be solved. This method is found to\nbe accurate and computationally efficient and enables us to consider binding\nenergy distribution even for a large gas-ice chemical network, which contains\nhundreds of icy species. The impact of the binding energy distribution on\ninterstellar ice composition is discussed quantitatively for the first time.","PeriodicalId":501209,"journal":{"name":"arXiv - PHYS - Earth and Planetary Astrophysics","volume":"95 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"A framework for incorporating binding energy distribution in gas-ice astrochemical models\",\"authors\":\"Kenji Furuya\",\"doi\":\"arxiv-2408.02958\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"One of the most serious limitations of current astrochemical models with the\\nrate equation (RE) approach is that only a single type of binding site is\\nconsidered in grain surface chemistry, although laboratory and quantum chemical\\nstudies have found that surfaces contain various binding sites with different\\npotential energy depths. When various sites exist, adsorbed species can be\\ntrapped in deep potential sites, increasing the resident time on the surface.\\nOn the other hand, adsorbed species can be populated in shallow sites,\\nactivating thermal hopping and thus two-body reactions even at low\\ntemperatures, where the thermal hopping from deeper sites is not activated.\\nSuch behavior cannot be described by the conventional RE approach. In this\\nwork, I present a framework for incorporating various binding sites (i.e.,\\nbinding energy distribution) in gas-ice astrochemical models as an extension of\\nthe conventional RE approach. I propose a simple method to estimate the\\nprobability density function for the occupation of various sites by adsorbed\\nspecies, assuming a quasi-steady state. By using thermal desorption and hopping\\nrates weighted by the probability density functions, the effect of binding\\nenergy distribution is incorporated into the RE approach without increasing the\\nnumber of ordinary differential equations to be solved. This method is found to\\nbe accurate and computationally efficient and enables us to consider binding\\nenergy distribution even for a large gas-ice chemical network, which contains\\nhundreds of icy species. The impact of the binding energy distribution on\\ninterstellar ice composition is discussed quantitatively for the first time.\",\"PeriodicalId\":501209,\"journal\":{\"name\":\"arXiv - PHYS - Earth and Planetary Astrophysics\",\"volume\":\"95 1\",\"pages\":\"\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2024-08-06\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"arXiv - PHYS - Earth and Planetary Astrophysics\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/arxiv-2408.02958\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - PHYS - Earth and Planetary Astrophysics","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2408.02958","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
摘要
目前采用速率方程(RE)方法的天体化学模型的一个最严重的局限性是在晶粒表面化学中只考虑了单一类型的结合位点,尽管实验室和量子化学研究已经发现,表面含有不同势能深度的各种结合位点。另一方面,被吸附的物种可以填充在浅层位点,激活热跳变,从而发生二体反应,即使在低温条件下,来自深层位点的热跳变也不会被激活。在这项工作中,我提出了一个将各种结合位点(即结合能分布)纳入气冰天体化学模型的框架,作为传统 RE 方法的扩展。我提出了一种简单的方法来估算吸附物种占据各种位点的概率密度函数,并假设其处于准稳态。通过使用由概率密度函数加权的热解吸附和跳板,结合能分布的影响被纳入 RE 方法,而无需增加需要求解的常微分方程的数量。该方法精确且计算效率高,使我们能够考虑结合能分布,即使是包含数百种冰物种的大型气冰化学网络。首次定量讨论了结合能分布对星际冰成分的影响。
A framework for incorporating binding energy distribution in gas-ice astrochemical models
One of the most serious limitations of current astrochemical models with the
rate equation (RE) approach is that only a single type of binding site is
considered in grain surface chemistry, although laboratory and quantum chemical
studies have found that surfaces contain various binding sites with different
potential energy depths. When various sites exist, adsorbed species can be
trapped in deep potential sites, increasing the resident time on the surface.
On the other hand, adsorbed species can be populated in shallow sites,
activating thermal hopping and thus two-body reactions even at low
temperatures, where the thermal hopping from deeper sites is not activated.
Such behavior cannot be described by the conventional RE approach. In this
work, I present a framework for incorporating various binding sites (i.e.,
binding energy distribution) in gas-ice astrochemical models as an extension of
the conventional RE approach. I propose a simple method to estimate the
probability density function for the occupation of various sites by adsorbed
species, assuming a quasi-steady state. By using thermal desorption and hopping
rates weighted by the probability density functions, the effect of binding
energy distribution is incorporated into the RE approach without increasing the
number of ordinary differential equations to be solved. This method is found to
be accurate and computationally efficient and enables us to consider binding
energy distribution even for a large gas-ice chemical network, which contains
hundreds of icy species. The impact of the binding energy distribution on
interstellar ice composition is discussed quantitatively for the first time.