Abstract:

OOD-RMPI spectroscopy Of ammonia using the fast predissoeiating à state as the intermediate has proved to be a feasible approach to uncover hidden spectroscopic information on both the upper electronic states and the intermediate predissociating species. The rotationally resolved MPI spectra of NH_3 and ND_3 X→(2hν_1)Ã→(hν_2)C′transition and correspondingly the rotational constants of ND_3 C′ ~1A_1′(v_2=0,1) haStebeen obtained. We found that only Q branch lines of NH_3 X→à 2-photon transition appeared when linearly polarised pumping light was used. At a series of different v_1 frequences, we can always get 2v_1+v_2 resonant with a fixed X→C′rovibronic transition line by tunning v_2. The intensity envelope of the ion signal thus obtained represents the rotational line profile of à state. From the width of the profile predissociation life time of à is obtained.