Resonance enhanced multiphoton ionization spectroscopy of NHD2 via the (B)over-tilde(1)E ''-state

Rotational analysis of the (2 + 1) resonance enhanced multiphoton ionization (REMPI) spectrum of the (B) over tilde E-1 '' Rydberg state of the ammonia isotopologue NHD2 is reported. While the electronic degeneracy is lifted in NHD2 the splitting is small enough that interactions between the two states must be considered, particularly to model the intensity of the transitions. A simple model is developed to account for these interactions, relating them to terms present in the symmetric isotopologues. Spectroscopic parameters for the zero point and (nu(2)' = 1-6) vibrational levels of the (B) over tilde E-1 '' state have been derived using this model and the spectra are accurately simulated for the first time using the PGOPHER program. The current work provides the basis for on-going velocity map imaging studies of rotational energy transfer in the mixed isotopologues of ammonia.