  Oscillations in time-dependent 2D electronic spectra appear as evidence of
quantum coherence in light-harvesting systems related to electronic-vibrational
resonant interactions. Nature, however, takes place in a non-equilibrium
steady-state, so the relevance of these arguments to the natural process is
unclear. Here we examine the role of intramolecular vibrations in the
non-equilibrium steady-state of photosynthetic dimers in the natural scenario
of incoherent light excitation. It is found that vibrations resonant with the
energy difference between exciton states do not increase the quantum yield nor
the imaginary part of the intersite coherence that is relevant for transport
compared with non-resonant vibrations in the natural non-equilibrium steady
state. That is, the vibration-electronic resonance interaction does not alter
energy transport under natural incoherent-light excitation conditions.
