Hot bands in overtone absorption of pyrrole, methyl isocyanide and isobutane: Photoacoustic spectra at 140 C

Isobutane Infrared Bands: Partial Rotational Assignments, ab Initio Calculations, and Local Mode Analysis

High-resolution infrared spectra of the symmetric top isobutane CH(CH₃)₃ were assigned with the help of ab initio calculations. The strong parallel band ν₅(a₁) with an origin at 1396.54741(76) cm^-1 and the ν₄(a₁) mode, the CH₂ scissors, at 1478.20363(41) cm^-1 were rotationally analyzed. The bands in the C-H stretching region were assigned with the help of an anharmonic calculation and a local mode analysis.

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.