Revealing the hot bands in the regions of the N-H and C-H stretch fundamentals of pyrrole.

Photoacoustic Raman spectra of gaseous pyrrole in the 3504-3535 and 3068-3152 cm(-1) energetic windows were measured, to obtain new information about the hot bands in the vicinity of the N-H(ν1) and C-H(ν2) stretch fundamentals, respectively. The observed vibrational patterns are characterized by sharp Q-branches, where the strong bands reflect the fundamentals and the weaker ones, as established from their temperature dependence, are hot bands. From the simulation of the observed spectra, the band origins and nondiagonal anharmonicities were determined. Comparison of the latter values to the anharmonicities, x(ij) (i = 1, 2 and j = 16, 15, 14, 12, 11) obtained from anharmonic calculations at the B3LYP/6-311++G(d,p), B3LYP/cc-pVQZ and MP2/cc-pVTZ levels, aided the tentative assignment of the hot bands. The retrieved parameters add new data to the extensive set of already known vibrational constants of pyrrole.