Formation of CH(+) is considered in the hot gas immediately behind shock fronts that may be present in the neutral gas clouds of the interstellar medium. Special attention is given to shocks which can result from expansion of the H II region around the stars toward which the observations are made. Column densities near 10 trillion per sq cm, in agreement with observations of diffuse clouds, are obtained for likely values of uncertain physical parameters. Column densities for other species, including CH, OH, and H2O, are also computed and are compatible with observations of diffuse clouds. Formation by shocks is thus proposed as a solution to the long-standing CH(+) abundance problem, which has been clarified by a recent laboratory measurement for the reaction rate of CH(+) + e.
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Elitzur et al. (1978) studied this question.