Chemistry of free radicals containing oxygen. Part 2.—Thermochemistry of the hydroxyl and hydroperoxyl radicals
Chemistry of free radicals containing oxygen. Part 2.—Thermochemistry of the hydroxyl and hydroperoxyl radicals
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DOI：
10.1039/tf9595500408
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发表时间：
1959
影响因子：
--
通讯作者：
P. Gray
中科院分区：
文献类型：
--
作者：
P. Gray
在动力学方案中最常调用的自由基是羟基HO和羟基H02。这两个物种在许多简单和复杂的系统中起着重要作用；例如，在氧+氢反应中，在碳氢化合物的燃烧中，在水的辐射分解中。为了评估它们的确切作用，需要对发生的个别反应提供可靠的热化学数据。过去已经对HO和HO2的生成热以及它们所参与的反应的焓变进行了大量的估计。一般来说，由于从标准状态的元素中生成€30和H02是实验上难以接近的过程，所以HO和HO2的生成焓的所有值都是通过结合其他热化学数据得出的，这些数据易于直接测定。这些都是“原始”数据。当然，直接实验并不是唯一的信息来源，也有人尝试基于理论前提或类比论证来推导HO和H02的生成焓。然而，当有实验证据时，它是首选的。HO的热化学所依据的主要数据是(i)其自身解离热和分子氢和氧解离成H和0原子的热的实验值，（ii）过氧化氢的生成焓及其解离成羟基自由基的热的实验值，以及（iii）水的生成焓的实验值和从水生成HO的反应热
Among free radicals most frequently invoked in kinetic schemes are hydroxyl HO and hydroperoxyl H02. These two species play important parts in many systems, simple and complex; for example, in the oxygen+ hydrogen reaction, in the combustion of hydrocarbons and in the radiolysis of water. For their exact role to be assessed, reliable thermochemical data are needed for the individual reactions occurring.Numerous estimates of the heats of formation of HO and HO2 and of enthalpy changes of reactions in which they take part have been made in the past. In general, since the formation of€ 30 and H02 from the elements in their standard states are experimentally inaccessible processes, all values for the enthalpies of formation of HO and HO2 are derived by the combination of other thermochemical data which are susceptible to direct determination. These are" primary" data. Of course, direct experiment is not the only source of information and attempts based on theoretical premises or on arguments of analogy have also been made to derive the enthalpies of formation of HO and H02. When experimental evidence is available, however, it is to be preferred. The primary data on which the thermochemistry of HO rests are (i) the experimental values of the heats of its own dissociation and of the dissociations of molecular hydrogen and oxygen into H and 0 atoms,(ii) experimental values of the enthalpy of formation of hydrogen peroxide and of its heat of dissociation into hydroxyl radicals and (iii) experimental values of the enthalpy of formation of water and heats of reaction producing HO from water such as