Infrared depletion spectroscopy suggests fast vibrational relaxation in the hydrogen-bonded aniline–tetrahydrofuran (C6H5–NH2⋯OC4H8) complex

The vibrational spectrum of the 1:1 aniline–tetrahydrofuran complex, formed in a pulsed supersonic jet, has been observed in the NH stretching region using IR depletion spectroscopy cum REMPI time-of-flight MS. Two strong absorption features observed at 3370 and 3479.3 cm−1 are assigned to the H-bonded and free N–H stretching vibrations of the complex, respectively. The vibrational frequencies and intensities of the NH stretching bands are qualitatively reproduced by ab initio MP2/6-31G∗∗ calculations. The optimized geometry shows one of the amino hydrogens of aniline interacts with the oxygen of tetrahydrofuran, giving a binding energy of 37 kJ mol−1 without BSSE correction. A fast vibrational relaxation occurs on vibrational excitation of the hydrogen-bonded N–H stretching mode.