  Single vibronic level (SVL) fluorescence spectroscopy contributes to the
understanding of molecular vibrational structures and relaxation processes.
Here, we present a practical method for computing SVL fluorescence spectra of
polyatomic molecules from arbitrary initial vibrational levels. This method,
which combines a time-dependent approach using Hagedorn wavepackets with
accurate evaluation of electronic structure, captures both mode distortion and
Duschinsky rotation. We apply the method to compute SVL spectra of anthracene
by performing wavepacket dynamics on a 66- dimensional harmonic potential
energy surface constructed from density functional theory calculations. With
the Hagedorn approach, we not only reproduce the previously reported simulation
results for singly excited $12^{1}$ and $\overline{11}^{1}$ levels, but also
are able to compute SVL spectra from multiply excited levels in good agreement
with experiments. All spectra were obtained from the same wavepacket trajectory
without any additional propagation beyond what is required for ground-state
emission spectra.
