MICROWAVE DETECTED, MICROWAVE-OPTICAL DOUBLE-RESONANCE OF NH3, NHD2, AND ND3 .1. STRUCTURE AND FORCE-FIELD OF THE (A)OVER-TILDE STATE

Microwave detected, microwave-optical double resonance was used to record the à 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 v2 excitation and an à state equilibrium bond length was estimated at 1.055(8) Å. In addition, the harmonic force field for the à state has been experimentally determined. fhh, fαα-fαα′, and frr were found to be 1.06(4) aJ/Å2, 0.25(2) aJ, and 4.9 aJ/Å2, respectively. This calculated harmonic force field predicts that the asymmetry observed in the NH3 24 band is due to a strong anharmonic interaction with the 43 level and the broad feature observed in the dispersed fluorescence spectrum previously assigned to the 11 band is more likely attributable to the 4 2 level. © 1995 American Institute of Physics.