从150到800 K二氧化碳的真空紫外吸收截面和对温暖的外行星大气的应用
VUV-absorption cross section of carbon dioxide from 150 to 800 K and applications to warm exoplanetary atmospheres
摘要：
迄今为止，大多数系外行星的大气温度都明显高于300 K。它们通常靠近恒星，接收强烈的紫外光子通量，从而触发重要的光解离过程。真空紫外吸收截面的T依赖性知之甚少，导致大气模型中的不确定性。类似地，在类似于火星、金星和土卫六的高层大气的低T下测量的数据往往缺乏。我们的目标是量化ABS的T依赖性。行星大气中重要分子的截面。我们希望提供高分辨率的数据在T盛行在这些媒体和一个简单的参数化的吸收，以简化其在光化学模型中的使用。这项研究的重点是二氧化碳。我们用同步辐射在115- 200 nm波长范围内测量了CO的$_2$吸收截面。对于较长的波长（195- 230 nm），我们使用氘灯和1. 5 mJobin-Yvon光谱仪。我们使用这些数据在我们的一维热光化学模式，以研究它们对预测的大气成分的影响。CO $_2$的截面随温度的升高而增大。它可以分为两个部分：连续体和叠加在连续体上的精细结构。连续吸收的变化可以用三个高斯函数的和来表示。在高温下使用热光化学模型的数据修改显着的丰度和许多物种的光解速率，除了CO $_2$，如甲烷和氨。这些偏差对合成透射光谱有影响，导致高达5 ppm的变化。本文给出了CO分子$_2$在115 ~ 230 nm范围内的HR（$Δλ$ =0.03nm）吸收截面，温度范围为150 ~ 800 K。
英文摘要：
Most exoplanets detected so far have atmospheric T significantly higher than 300K. Often close to their star, they receive an intense UV photons flux that triggers important photodissociation processes. The T dependency of VUV absorption cross sections are poorly known, leading to an undefined uncertainty in atmospheric models. Similarly, data measured at low T similar to that of the high atmosphere of Mars, Venus, and Titan are often lacking. Our aim is to quantify the T dependency of the abs. cross section of important molecules in planetary atmospheres. We want to provide both high-resolution data at T prevailing in these media and a simple parameterization of the absorption in order to simplify its use in photochemical models. This study focuses on carbon dioxide. We performed experimental measurements of CO$_2$ absorption cross section with synchrotron radiation for the wavelength range (115--200nm). For longer wavelengths (195--230nm), we used a deuterium lamp and a 1.5m Jobin-Yvon spectrometer. We used these data in our 1D thermo-photochemical model in order to study their impact on the predicted atmospheric compositions. The cross section of CO$_2$ increases with T. It can be separated in two parts: a continuum and a fine structure superimposed on the continuum. The variation of the continuum of absorption can be represented by the sum of three gaussian functions. Using data at high T in thermo-photochemical models modifies significantly the abundance and the photodissociation rates of many species, in addition to CO$_2$, such as methane and ammonia. These deviations have an impact on synthetic transmission spectra, leading to variations of up to 5 ppm. We present a full set of HR ($Δλ$=0.03nm) absorption cross sections of CO$_2$ from 115 to 230nm for T ranging from 150 to 800K.
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