Warm neutral halos around molecular clouds. V - OH (1665 and 1667 MHz) observations

Ten strip maps of 1665- and 1667-MHz OH emission, traversing the outer boundaries of five molecular clouds, were made. The OH emission is found to be significantly extended relative to CO, from which it inferred that OH is to be found in abundance in the shell of partly atomic, partly molecular gas surrounding the dense molecular clouds. The fractional OH abundance is calculated using existing H I and CO observations, and detailed source models which include a complete chemistry network and a radiative transfer code. It is concluded that the extended OH is formed, not by the exothermic reaction of O with H3(+), but by the endothermic reaction, H(+) + O yields H + O(+).