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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 B3LYP/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.

Microwave spectra and structure of an isoxazole-CO Van der Waals complex The spectroscopy and single vibronic level fluorescence quantum yields of jet cooled transstilbene and its van der Waals complexes J. Chem. Phys. 78, 5493 (1983); 10.1063/1.445477Fluorescence excitation spectrum of stetrazine cooled in a supersonic free jet: Van der waals complexes and isotopic species

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