SPECTROSCOPY AND EXCITED-STATE DYNAMICS OF THE HNF (DNF) MOLECULE

Laser fluorescence excitation has been employed to detect HNF and its isotopomer DNF in the F/HN3 (DN3) system. The observation of this molecule in the F + HN3 reaction has confirmed that this reaction proceeds to form HNF + N2, as well as the well-known HF + N3 products. Laser fluorescence excitation scans were taken for a number of HNF and DNF A 2A'(0,v2',0)-X 2A" (0,0,0) bands. For DNF, excitation of the A (0,2,1) and (0,3,1) levels were also detected. A partial rotational analysis of the DNF bands was carried out. With the derived A rotational constants and previously determined HNF rotational constants, it was possible to derive ground and excited state vibrationally averaged geometries. The K structure of the bands was observed to become simpler with increasing v2', reflecting the reduction in the highest K' levels observable by fluorescence excitation. Decay lifetimes for a variety of HNF and DNF A 2A' excited levels were determined. It was found that the decay rate, scaled approximately by the v3 factor, increases abruptly at an energy of 23 800 +/- 500 cm-1 above the HNF (X 2A") zero-point level. This threshold is tentatively assigned to the onset of a predissociation channel. The ground and excited states of HNF form a Renner-Teller pair, whose energies become degenerate at linear geometries. The excited state dynamics of HNF (DNF) is compared with the dynamics of the well-studied Renner-Teller molecules HCO and HNO.