Spectroscopic, ab initio, and Smog-Chamber Studies of Molecular Aggregates

该研究计划描述了一个研究分子聚集体的计划，这些聚集体与大气化学有关，跨越了从微观、分子世界到纳米尺度的大小范围。高分辨率旋转光谱学的革命性进展使得对较小的络合物和团簇的研究成为可能，无论是在开发强大的光谱技术方面，还是在开发有效的软件以帮助进行复杂的光谱分配过程方面。这些研究的核心是对“临界核”的描述，它在大气气溶胶粒子的形成和生长中起着至关重要的作用。这些关键的原子核被认为由几个分子组成，包括有机酸、硫酸和水，但到目前为止还没有提供“微观”的光谱分析。 氦纳米液滴可以由大约1000到数百万个氦原子组成，达到~0.4K的温度，并且是超流体。这些性质使它们成为研究不稳定分子和低温反应的理想基质。许多大气反应涉及自由基，是无障碍的或具有低障碍的。除了自由基反应，例如甲苯自由基和分子氧之间的反应，我们还将研究光诱导反应。一个例子是草酸的光致分解，草酸是大气中含量最丰富的二元酸，它可能是这类化合物在大气中的主要汇。 即使是更大的系统，即二次有机气溶胶颗粒和烟尘颗粒，也将使用光反应或烟雾室进行研究。例如，煤烟颗粒是在不完全的化石燃料燃烧中产生的，并被大量排放到大气中。尤其令人感兴趣的是烟尘颗粒的老化过程。大气中的烟尘可以被二次有机气溶胶覆盖，这种二次有机气溶胶可能是由化石燃料燃烧过程中释放的有机物质产生的。这种涂层不仅改变了颗粒的表面性质，而且表面张力的增加会导致碳烟核心的崩溃。涂层和坍塌都会导致光学性质的变化，并影响烟尘颗粒对辐射强迫的贡献。 拟议的研究将导致对大气过程有更深入的了解，包括气溶胶颗粒的增长和老化，其结果将对大气建模产生影响，并可能减少与气溶胶对全球气候的直接和间接影响有关的不确定性。

The research proposal describes a program to study molecular aggregates, which are of relevance to atmospheric chemistry, spanning size regimes from the microscopic, molecular world to the nano-scale. The proposed studies on smaller complexes and clusters are enabled by revolutionary advances in high-resolution rotational spectroscopy in terms of both the development of powerful spectroscopic techniques and developments of effective software to aid in the complex spectroscopic assignment processes. At the heart of theses studies is the characterization of 'critical nuclei', which play a crucial role in the formation and growth of atmospheric aerosol particles. These critical nuclei are thought to consist of several molecules, including organic acids, sulfuric acid, and water, but 'microscopic', spectroscopic analyses have thus far not been provided. Helium nanodroplets can consist of about a thousand to millions of helium atoms, attain a temperature of ~0.4 K, and are superfluid. These properties make them an 'ideal' matrix to study not only unstable molecules, but also low-temperature reactions. Many atmospheric reactions involve radicals and are barrier-less or have low barriers. In addition to radical reactions, for example, between tolyl radical and molecular oxygen, we will also investigate photo-induced reactions. An example is the photo-induced decomposition of oxalic acid, the most abundant dicarboxylic acid in the atmosphere, which could be a major atmospheric sink for this type of compounds. Even larger systems, namely secondary organic aerosol particles and soot particles, will be studied using a photo-reaction or 'smog' chamber. Soot particles are produced in incomplete fossil fuel combustion, for example, and are emitted in great quantities into the atmosphere. Of particular interest is the ageing process of soot particles. Atmospheric soot can be coated with secondary organic aerosol, perhaps produced from organic material also released during fossil fuel burning. This coating changes not only the surface properties of the particle but the increased surface tension causes a collapse of the soot core. Both coating and collapse lead to changes in optical properties and affect the contributions of soot particles to radiative forcing. The proposed research will lead to greater insights into atmospheric processes, including aerosol particle growth and ageing, and the results will have impact on atmospheric modelling and will likely reduce the uncertainties associated with the direct and indirect effects of aerosol on the global climate.