Detailed Dynamics of Atmospheric Photoreactions

小行星9725549 羟基自由基（OH）是大气中碳氢化合物和一氧化碳被氧化的主要途径。 有一个模型之间的差异计算的OH增加的时间依赖性以下日出和观测，特别是在平流层较低。 在黎明时分，模型始终低估了测量的OH浓度;特别是在黎明时分，测量的OH浓度突然增加，接近最大量的20%（发生在中午），这是模型无法预测的。 为了应对这些不确定性，该项目将理论和实验室实验联系起来，研究大气光反应的详细动力学。具体而言，两个领域的调查概述为潜在的提供大气自由基与太阳光子的能量比标准模型中假设的低得多。这些领域包括：1）使用实验和理论技术相结合的方法，研究主要大气化学物质（硝酸、过硝酸、过氧化氢、水）中OH伸缩振动泛音跃迁的可见激发的一般机制; 2）通过实验室研究检查分子复合物的振动和电子光谱。 这项工作的成果，预计将是改进的参数化的小分子光反应和分子簇动力学列入化学模型的大气。

9725549 Vaida The hydoxyl radical (OH) is the primary means by which hydrocarbons and carbon monoxide are oxidized in the atmosphere. There is a discrepancy between model calculations of the time dependence of the OH increase following sunrise and observations, particularly in the lower stratosphere. At dawn, the models consistently underestimate the measured OH concentration; in particular, at daybreak there is a sudden increase in the measured OH concentration, amounting to close to 20 percent of the maximum amount (occurring at noon), which is not predicted by models. In response to these uncertainties, the project links theory and laboratory experiments to study the detailed dynamics of atmospheric photoreactions. Specifically, two areas of inquiry are outlined as potentially providing atmospheric free radicals with solar photons of much lower energy than assumed in standard models. These areas involve: 1) investigation of a general mechanism involving visible excitation of overtone transitions of the OH stretching vibrations in key atmospheric chemical species (nitric acid, pernitric acid, hydrogen peroxide, water) using a combination of experimental and theoretical techniques; and 2) examination of the vibrational and electronic spectra of molecular complexes through laboratory investigations. The outcome of this work is expected to be the improved parameterizations of small molecule photoreactions and molecular cluster dynamics for inclusion in chemical models of the atmosphere.