Oxygen absorption spectrum, cross section

Fig. 2-6. Ultraviolet absorption spectrum of molecular oxygen, with cross sections given in units of cm2/molecule. Data compiled from Ackerman and Biaume (1970), Ditchburn and Young (1962), Hudson ei al. (1966), Ogawa (1971), Shardanand (1969), Shardanand and Rao (1977), and Watanabe et al. (1953).

As the absorption spectrum, absorption cross sections, and potential curves has already been described in Chap. 3 (Sect. 3.2, Fig. 3.4, 3.5, Table 3.2), only photolytic processes will be discussed here. In the photolysis of O2, three different electronic states of oxygen atoms can be formed as follows. 

In very rare cases in which photoionization is the only photoprocess, the absorption observed in a nitrous oxide-saturated solution will be that of the cation radical. However, generally, other processes such as intersystem crossing also occur in parallel. In the presence of oxygen, the hydrated electron and the triplet will be scavenged at diffusion-controlled rates, and the absorption observed in the oxygenated solution will be due to the cation radical. Under these conditions, the cation radical spectrum is easily determined. The molar absorption coefficient of the cation radical can also be calculated using the hydrated electron as an internal standard. The molar absorption coefficient for sulphacetamide cation radical was determined in this manner (Land et al 1982) and later confirmed by pulse radiolysis (see Section 12.2.2.6). 

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