  We have combined ab initio quantum chemistry calculations with a
rate-equation formalism to analyze electroluminescence spectra in
single-molecule junctions, measured recently by several groups in Scanning
Tunneling Microscope setups. In our method, the entire vibrational spectrum is
taken into account. Our method leads to good quantitative agreement with both
the spectroscopic features of the measurements and their current and voltage
dependence. Moreover, our method is able to explain several previously
unexplained features. We show that in general, the quantum yield is expected to
be suppressed at high bias, as is observed in one of the measurements.
Additionally, we comment on the influence of the vibrational relaxation times
on several features of the spectrum.
