In this work we demonstrate that a doubly hydrogen-bonded interface of two carboxylic acid groups behaves as efficient conduit to transmit the rotor effects for IVR acceleration in a phenyl ring. The phenomenon has been demonstrated by measuring the resolved emission spectra following SVL excitations in S-1 of a 1:1 mixed dimer between acetic acid and benzoic acid. The role of the methyl rotor has been ascertained by comparing the results with those obtained for an analogous dimeric system between formic acid and benzoic acid.(C) 2004 American Institute of Physics.