Vibrational overtone spectroscopy of pyrrole and pyrrolidine

Abstract

Abstract : The gaseous near infrared and visible absorption spectra of pyrrole and pyrrolidine have been measured for the first through fourth N-H stretch vibrational overtones and the second through fourth C-H stretch overtones. The C-H overtone features follow the simple local mode expression with anharmonicites of 52 cm-1 for pyrrole and 55 cm-1 for pyrrolidine. Multiple transitions observed in the N-H stretching regions indicate the presence of vibrational coupling to other vibrational modes. For comparison, the visible spectra of neat liquid pyrrole, dilutions of pyrrole in carbon tetrachloride, and neat liquid pyrrolidine were obtained by direct absorption spectroscopy. The pattern of multiple peaks for the N-H absorption region appears (shifted 200 cm- 1 to the red) in solution phase pyrrole. This shift of all the peaks results from the intermolecular interactions of the N-H in the liquid; however, the preservation of the peak splittings indicates that this splitting is a result of intramolecular vibrational coupling.