NH stretching vibrations of pyrrole clusters studied by infrared cavity ringdown spectroscopy

• Published in: The Journal of chemical physics 2007-11, Vol.127 (18), p.184310-184310-9
• Main Authors: Matsumoto, Yoshiteru, Honma, Kenji
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.2790894

The IR spectra for various sizes of pyrrole clusters were measured in the NH stretching vibration region by infrared cavity ringdown spectroscopy. The hydrogen-bonded structures and normal modes of the pyrrole clusters were analyzed by a density functional theory calculation of the B 3 LYP ∕ 6 - 311 + G ( d , p ) level. Two types of pulsed nozzles, a slit and a large pinhole, were used to generate different cluster size distributions in a supersonic jet. A rotational contour analysis of the NH stretching vibration for the monomer revealed that the slit nozzle provides a warmer jet condition than the pinhole one. The IR spectra, measured under the warmer condition, showed the intense bands at 3444, 3392, and 3382 cm − 1 , which were assigned to hydrogen-bonded NH stretching vibrations due to the dimer, the trimer, and the tetramer, respectively. On the other hand, the IR spectra measured under a lower temperature condition by a pinhole nozzle showed a broad absorption feature in addition to sharp bands. This broad absorption was reproduced by the sum of two Gaussians peaks at 3400 and 3372 cm − 1 with widths of 30 and 50 cm − 1 (FWHM), respectively. Compared with the spectra of the condensed phase, two bands at 3400 and 3372 cm − 1 were assigned to hydrogen-bonded NH stretching vibrations of larger clusters having liquid-like and solid-like structures, respectively.