Laboratory Studies Required to Understand Cometary Emissions: O(1S) and O(1D) Yields from CO2 Photodissociation in the Extreme Ultraviolet

该奖项的主要目标是产生可靠地解释和量化彗星二氧化碳排放所需的实验室测量结果。彗星是相对较小的天体，由冰和泥土组成，围绕太阳运行；然而，它们大部分时间都远离太阳，温度非常低。因此，它们被认为是太阳系中保存最好、最原始的物体之一，它们的化学成分是限制太阳系形成模型的关键。人们对二氧化碳特别感兴趣，因为这种分子可能在彗星核中以足够高的数量存在，以至于升华（在加热时直接从冰变成气体，而不会变成液态水）可能是彗星靠近太阳轨道时活动的一个重要部分。PI和他的研究小组将进行实验，以更好地了解二氧化碳从靠近太阳的彗星核升华后如何在阳光下降解。该项目的重点是在彗星光谱中经常观察到的两个原子氧发射线，它们可能主要是在二氧化碳分解期间形成的。由于地面望远镜无法观测到二氧化碳，因此原子氧发射线可以作为二氧化碳的有价值的代表。这项工作也将有助于建立火星、金星和一些系外行星的大气模型。PI将培训和指导一名博士后和暑期本科生进行这项研究。计划中的实验将在劳伦斯伯克利国家实验室的先进光源中进行。该团队将使用同步辐射来测定90-115 nm二氧化碳光解的O（1S）和O（1D）产量。为了扩大对这两种通常具有长辐射寿命的原子状态的检测，他们将向样品中引入氙气，这将辐射率提高了75倍。对二氧化碳光解作用激发的原子氧谱线的了解，将使利用原子氧的红色和绿色谱线发射（分别为630/636.4 nm和557.7 nm）作为彗星成分的探测成为可能。

This award's main goal is to produce laboratory measurements that are needed to reliably interpret and quantify carbon dioxide emissions from comets. Comets are relatively small bodies made of ice and dirt that orbit the Sun; however, they spend most of their time very far from the Sun at very cold temperatures. Thus, they are considered to be among the best preserved and most primordial objects in the solar system and their chemical composition is key to constraining solar system formation models. Carbon dioxide is of particular interest because the molecule may be present in comet nuclei in high enough quantities that sublimation (going directly from ice to gas upon heating without ever becoming liquid water) may drive a significant portion of the activity as comets orbit close to the Sun. The PI and his research team will conduct experiments in order to better understand how carbon dioxide degrades in sunlight after sublimating from comet nuclei that are close to the Sun. The project focuses on two atomic oxygen emission lines commonly observed in comet spectra, which are possibly largely formed during the breakup of carbon dioxide. Since carbon dioxide is unobservable from ground-based telescopes, the atomic oxygen emission lines serve as a valuable proxy for carbon dioxide. This work will also be useful for modeling atmospheres of Mars, Venus and some exoplanets. The PI will train and mentor a postdoctoral fellow and summer undergraduate students in this research. The planned experiments will be carried out at the Advanced Light Source of the Lawrence Berkeley National Laboratory. The team will use synchrotron radiation to determine O(1S) and O(1D) yields from carbon dioxide photodissociation at 90-115 nm. In order to amplify detection of these two atomic states, which normally have long radiative lifetimes, they will introduce xenon gas to the samples, which enhances the radiative rate by a factor of 75. Knowledge of these excited atomic oxygen lines from carbon dioxide photodissociation will enable the use of the atomic oxygen red and green line emissions (at 630/636.4 nm and 557.7 nm, respectively) as a probe of cometary composition.