The continuous absorption spectrum of methyl bromide and its quantal interpretation

Abstract

Of organic compounds exhibiting continuous absorption, methyl bromide is one of the simplest and its spectrum is one most easily analysed quantum mechanically. This communication describes measurements of the extinc­tion coefficients of methyl bromide over a wide range and a calculation from them of the position of the upper potential energy curve. As the absorption band is continuous, this upper potential energy curve is of the repulsive type. Most of the previous work on methyl bromide deals with the band system in the Schumann region. Herzberg and Scheibe (1930), however, investigated the continuous absorption from 42,000 to 60,000 cm. -1 and found a maximum at 50,300 cm. -1 . Henrici (1932) found a maximum at 51,400 cm. -1 and estimated the absorption limit to be at 41,400 cm. -1 . Hukumoto (1932) also estimated the absorption limit and hence calculated the heat of dissociation, but it is now known that no well-defined absorption limit exists. All the previous workers concluded that methyl bromide dissociates into a methyl radical and a bromine atom, one or both of the products being excited. As will be shown in § 13 below, there is no justification for such a conclusion.