Microwave optical double resonance spectrum of NH2. V. Hyperfine structure of the u state

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Abstract
The hyperfine structure of the u state of NH2, a rovibronic level in the ? 2B1 manifold [tentatively assigned as 220, J=3/2, ? 2B1(0,13,0)] has been obtained from an analysis of the strong microwave optical double resonance (MODR) signals which occur between the u state and the J=1/2 and 3/2 spin components of 110 in ?2 A1Π (0,10,0). The hyperfine assignment was verified with a new technique that we have chosen to call microwave modulated saturation (MMS) spectroscopy. The similarity of the hyperfine splittings in u due to the H nuclear spin with those of the 220, J=3/2 rotational level of the ? 2B1(0,0,0) state supports the assignment of u to a highly excited vibrational state of ? 2B1. The hyperfine splittings due to the 14N nucleus were found to be about 1 MHz. These splittings are considerably smaller than those of 220 X 2B1(0,0,0) (which are about 6–10 MHz). This difference has been attributed to the fact that the hyperfine coupling constants of (0,13,0) must be averaged over a large amplitude bending motion and to the presence of borrowed ? 2A1 character in the u state.