MICROWAVE OPTICAL DOUBLE-RESONANCE SPECTRUM OF NH2 .5. HYPERFINE-STRUCTURE OF THE U-STATE

The hyperfine structure of the u state of NH2, a rovibronic level in the X 2B, manifold [tentatively assigned as 220, J = 3/2, X2B1(O,13,O)] 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 A 2Π(O,10,O). 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 X 2B1(O,O,O) state supports the assignment of u to a highly excited vibrational state of X2B1. 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(O1O1O) (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 A∼2A1 character in the u state. © 1979 American Institute of Physics.