Spectroscopy and Chemistry of Jet-Cooled Free Radicals

这项有机和大分子化学计划的拨款支持科罗拉多大学G. Barney Ellison博士研究喷气冷却有机自由基的红外吸收光谱。自由基与离子的反应也将在快流反应器中进行研究。自由基是一种不稳定的反应中间体，在许多燃烧过程和高温等离子体中起着至关重要的作用；需要光谱探针来监测这些亚稳态物种的命运。该企业将发展一项实验，使通过自由射流膨胀制备强基束成为可能。自由基如甲基、烯丙基和氰甲基可以通过各种光化学和热源制备。光源将由光电离质谱仪监测。在1 mTorr量级的自由基密度将被制备，这些反应物质将被射流冷却到大约20 K的旋转温度。这些自由基将用红外吸收光谱法与FTIR进行研究。选择的研究是甲基自由基家族：甲基，氟甲基，二氟甲基，三氟甲基和氰甲基。在所有情况下，计划建立分子的几何形状和振动频率。烯丙基自由基也同样令人感兴趣，因为它是最简单的共轭烃。干净的、特征化的自由基束将用于研究负离子（如氢氧化物离子或甲氧基离子）和碳氢化合物自由基（如烯丙基或苯基）之间的反应。埃里森博士希望建立烯丙基的气相酸度，以与丙烯或甲苯进行对比。单独的实验将使用这些自由基源来研究甲基自由基在干净的金或石墨表面上的散射。这将建立这些自由基的粘附系数以及分子沉积速率。

This grant in the Organic and Macromolecular Chemistry Program supports research of Dr. G. Barney Ellison, University of Colorado, to study the infrared absorption spectroscopy of jet-cooled organic radicals. The reactions of radicals with ions will also be studied in a fast flow reactor. Radicals are unstable reactive intermediates which are of paramount importance in many combustion processes and high temperature plasmas; spectroscopic probes are needed to monitor the fate of these metastable species. The enterprise is to develop an experiment which will enable preparation of intense radical beams via a free jet expansion. Radicals such as methyl, allyl, and cyanomethyl will be prepared by a variety of photochemical and thermal sources. Sources will be monitored by a photoionization mass spectrometer. Radical densities on the order of 1 mTorr will be prepared and these reactive species will be cooled by the jet to rotational temperatures of about 20 K. These radicals will be investigated by infrared absorption spectroscopy with an FTIR. Selected for study are the family of methyl radicals: methyl, fluoromethyl, difluoromethyl, trifluoromethyl, and cyanomethyl. In all cases, it is planned to establish the molecular geometries and vibrational frequencies. The allyl radical is of similar interest since it is the simplest conjugated hydrocarbon. Clean, characterized radical beams will be used to study the reactions between negative ions, such as hydroxide ion or methoxide ion, and hydrocarbon radicals such as allyl or benzyl. Dr. Ellison hopes to establish the gas phase acidity of allyl to contrast with propene or toluene. Separate experiments will use these radical sources to study the scattering of methyl radicals off clean gold or graphite surfaces. This will establish the sticking coefficients of these radicals as well as the rate of molecular deposition.