Kinetics of astrochemical reactions at very low temperatures

将使用实验和计算方法探索关键气相天体化学反应的化学机制。该项目的实验部分涉及使用脉冲拉瓦尔喷嘴装置，使用激光闪光光解结合激光诱导荧光（LIF）光谱学研究反应的动力学温度下降到25 K左右（我们的设备的电流极限），接近星际空间中遇到的。将测量小自由基（例如OH、碳基自由基（例如CN）和氮基自由基（例如NH2））与在含有一系列官能团的空间中发现的有机分子的反应的速率系数k（T）。为了补充实验，这些反应的势能面（PES）将使用高斯计算机程序套件或其他方法通过从头算方法计算。PES然后将用于计算速率系数作为温度和压力的函数，使用在利兹开发的MESMER速率理论软件包。MESMER还将允许在可实现的实验条件之外计算速率系数，例如低至10 K，并且将使得能够计算作为温度和压力的函数的产物支化比。理论预测与实验测量的比较将使PES的细节得到优化，反应机制的假设得到验证。该项目还将开发k（T）的参数化，并在天体化学模型中使用这些参数来计算复杂有机分子的丰度，以便与天文望远镜观测结果进行比较。这将提高我们对空间化学过程的理解，这些化学过程控制复杂有机分子的形成和破坏，其中一些可能与益生元分子有关，这是它们丰富的原因。

The chemical mechanisms of key gas-phase astrochemical reactions using both experimental and computational methods will be explored. The experimental part of the project involves using a pulsed Laval nozzle apparatus using laser flash-photolysis combined with laser-induced fluorescence (LIF) spectroscopy to study the kinetics of reactions down to temperatures around 25 K (the current limit of our apparatus), close to those encountered in interstellar space. Rate coefficients, k(T), will be measured for reactions of small free-radicals, for example OH, carbon-based radicals (e.g. CN) and nitrogen-based radicals (e.g. NH2) with organic molecules found in space containing a range of functional groups. To complement the experiments, the potential energy surfaces (PESs) for these reactions will be calculated by ab initio methods utilising the Gaussian suite of computer programmes, or other methods. The PESs will then be used to compute rate coefficients as a function of temperature and pressure, using the MESMER rate theory software package developed at Leeds. MESMER will also allow rate coefficients to be calculated outside of achievable experimental conditions, for example down to 10 K, and will enable the calculation of product branching ratios as a function of temperature and pressure. A comparison of theoretical predictions with experimental measurements will enable details of the PESs to be optimised and hypotheses for reaction mechanisms to be validated. The project will also develop parameterisations for k(T) and use these in astrochemical models to calculate the abundance of complex organic molecules for comparison with astronomical telescope observations. This will improve our understanding of the chemical processes in space which control the formation of destruction of complex organic molecules, some of which may link to prebiotic molecules, which account for their abundance.