Detailed Dynamics of Atmospheric Photoreactions

9725549羟基自由基(OH)是碳氢化合物和一氧化碳在大气中被氧化的主要途径。日出后OH增加的时间依赖关系的模型计算与观测之间存在差异，特别是在平流层低层。在黎明时分，模型总是低估了测量到的OH浓度；特别是在黎明时，测量到的OH浓度突然增加，达到最大值(发生在中午)的20%，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。具体地说，有两个研究领域被概述为可能为大气自由基提供比标准模型中假设的能量低得多的太阳光子。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种(硝酸、过硝酸、过氧化氢、水)中OH伸缩振动的泛音跃迁的一般机制；以及2)通过实验室研究来检查分子络合物的振动和电子光谱。预计这项工作的结果将是小分子光反应和分子团簇动力学的改进的参数化，以便纳入大气化学模型。

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.