The microwave spectrum of the NH2 radical: The hyperfine structure of the B-2(1) ground electronic state

The pure rotational spectrum of the NH2 radical in its (X) over tilde B-2(1) ground electronic state was measured in the frequency region of 230-470 GHz by microwave spectroscopy. The radical was generated in a free space cell by de-glow discharge of NH3. Seventy nine fine and hyperfine components of four rotational transitions were measured, and were analyzed by least squares methods. The hyperfine coupling constants for both the nitrogen and hydrogen nuclei were redetermined with higher precision than those of the previous analysis for microwave optical double resonance (MODR) data. The nuclear spin-rotation constants for the hydrogen nucleus as well as the nitrogen nucleus were found to be anomalously large. The anomalous constant of C-aa(H) is interpreted by the same reason for the anomalous large value for C-aa(N) originating from the large A constant and the relatively low-lying (A) over tilde (2)A(1) electronic state. (C) 1997 American institute of Physics.