THE NH STRETCH IN PYRROLE - A STUDY OF THE FUNDAMENTAL (DELTA-V=1) AND 3RD OVERTONE (DELTA-V=4) BANDS IN THE BULK GAS AND IN A MOLECULAR-BEAM

We have examined the NH stretching vibration in pyrrole both in the infrared and visible regions of the spectrum. Three techniques were used-direct absorption spectroscopy, intracavity photoacoustic spectroscopy, and optothermal molecular beam spectroscopy. In the bulk gas, the DELTA-upsilon = 1 transition is composed of a well-resolved manifold of subbands. Molecular beam spectra of a number of those subbands reveal detailed structure due to single state-to-state transitions. An asymmetric rotor model was found to provide an adequate description of the spectra and a complete set of rotational parameters has been determined. Little evidence of rotational perturbations was observed in the DELTA-upsilon = 1 spectrum. The bulk gas DELTA-upsilon = 4 overtone band is composed of three vibrational transitions, whose rotational contours overlap. These transitions involve Fermi resonance among assignable NH and CH stretching excited states. Attempts to detect DELTA-upsilon = 4 overtone transitions on the molecular beam failed, in spite of the large anticipated signal-to-noise ratio calculated by extrapolation from the DELTA-upsilon = 1 data. This negative result is a likely consequence of extensive level mixing in the DELTA-upsilon = 4 region.