In the paper we report the first observation of the vibrational spectrum in the B-H stretching region in the gas phase for a dihydrogen bonded complex. The appearance of three transitions for the B-H stretching modes of a (di)hydrogen-bonded complex involving borane-trimethylamine indicates the lowering of the symmetry on the BH3 group upon interaction with phenol. Further, the shift in the O-H stretching frequency indicates that phenol is hydrogen bonded to borane-trimethylamine. The two sets of the present data establish, unequivocally, the formation of O-H…H-B dihydrogen-bonded complex between phenol and borane-trimethylamine.