Infrared depletion spectroscopy of the doubly hydrogen-bonded aniline-(tetrahydrofuran)2 complex produced in supersonic jet

The vibrational frequencies of the N-H stretching modes of aniline after forming a strong doubly H-bonded complex with tetrahydrofuran (THF) are measured with infrared depletion spectroscopy that uses cluster-size-selective resonance-enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometry. Two strong infrared absorption features observed at 3355 and 3488 cm−1 are assigned to the symmetric and antisymmetric N-H stretching vibrations of the 1:2 aniline-THF complex, respectively. The red-shifts of the N-H stretching vibrations of aniline agree with the ab initio calculated (MP2/6-31G**) aniline-(THF)2 structure in which both aniline N-H bonds interact with the oxygen atom of THF through two hydrogen bonds. The calculated binding energy is found to be 29.6 kJ mol−1 after corrections for basis set superposition error (BSSE) and zero-point energy. The calculated structure revealed that the angle between the N-H bonds in the NH2 group increased to 112.5° in the aniline-(THF)2 complex from that of 109.8° in the aniline. The electronic 0-0 band origin for the S1 ← S0 transition is observed at 32,900 cm−1 in the aniline-(THF)2 complex, giving a red-shift of 1129 cm−1 from that of the aniline molecule.