  Microwave detected, microwave-optical double resonance was used to record the
A state electronic spectrum of NH3, NH2D, and NHD2 with both vibrational and
rotational resolution. To investigate ND3 with the same resolution as we had
with our hydrogen containing isotopomers, a strip-line cell was constructed
allowing the simultaneous passage of radio-frequency and ultraviolet radiation.
Rotational constants were obtained as a function of nu2 excitation and an A
state equilibrium bond length was estimated at 1.055(8) angstroms. In addition,
the harmonic force field for the A state has been experimentally determined.
fhh, falpha,alpha-falpha,alpha', and frr were found to be 1.06(4)aJ/angstrom2,
0.25(2)aJ, and 4.9aJ/angstrom^2 respectively. This calculated harmonic force
field predicts that the asymmetry observed in the NH3 2(4) band is due to a
strong anharmonic interaction with the 4(3) level and the broad feature
observed in the dispersed fluorescence spectrum previously assigned to the 1(1)
band is more likely attributable to the 4(2) level.
