Hydrogen Emission Line n110 → n109: Detection at 5009 Megahertz in Galactic H II Regions

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Science  15 Oct 1965:
Vol. 150, Issue 3694, pp. 339-348
DOI: 10.1126/science.150.3694.339


The hydrogen emission line n1l0 → n109 at the frequency 5009 megahertz which was predicted by Kardashev has been detected in M 17, Orion, and nine other galactic H II regions with the 42.7-m (140-foot) telescope and a 20-channel receiver at the National Radio Astronomy Observatory. The measured product of the half-power width of the line times the ratio of line-to-continuum brightness temperature is larger than that predicted by Kardashev's theory. The radial velocity obtained for M 17 and Orion agrees well with optical measurements. The search for a similar line of excited helium was without success.