A radio recombination line the spectrum of W44

A H 1 66a recombination line was found in the continuum spectrum of W44 and in the weak galactic emission about three-quarters of a degree away. The lines are weak, but there is a difference in their structure. The recombination-line parameters are compared with the neutral hydrogen and molecular line parameters. It is suggested that the supernova explosion of W44 may be responsible for ionizing the gas which is emitting the H 1 66e line. This possibility is discussed; however, it is concluded that due to insufficient observations, emission from diffuse gas not associated with W44 or from an H ii region that has line-of-sight coincidence with W44 cannot be ruled out. The absence of H 1 66a absorption or stimulated emission is used to estimate upper limits to the ionization rate of the gas in front of W44. These limits are compatible with other published estimates of the ionization rate of the interstellar material. Subject headings: interstellar matter - nebulae - radio lines - supernovae