The fluorescence and resonance Raman emission of molecular systems undergoing ultrafast nonadiabatic isomerization is considered. Adopting a multidimensional model of vibronic coupling, explicit expressions for the continuous-wave spectra as well as for the time-resolved fluorescence spectrum are derived. To facilitate a simple eigenstate-free evaluation of the spectra of interest, various approximations are introduced. Employing a two-mode, two-state model of the photoisomerization of retinal, the validity of the approximations is studied numerically. The time-dependent eigenstate-free scheme is shown to provide an accurate approximation to the exact fluorescence spectrum. On the other hand, the well-known assumption that the emission stems from a vibrationally relaxed excited electronic state is not applicable in the case of ultrafast nonadiabatic isomerization processes under consideration.