  We have investigated the photodynamics of $\beta$-D-glucose employing our
field-induced surface hopping method (FISH), which allows us to simulate the
coupled electron-nuclear dynamics, including explicitly nonadiabatic effects
and light-induced excitation. Our results reveal that from the initially
populated S$_{1}$ and S$_{2}$ states, glucose returns nonradiatively to the
ground state within about 200 fs. This takes place mainly via conical
intersections (CIs) whose geometries in most cases involve the elongation of a
single O-H bond, while in some instances ring-opening due to dissociation of a
C-O bond is observed. Experimentally, excitation to a distinct excited
electronic state is improbable due to the presence of a dense manifold of
states bearing similar oscillator strengths. Our FISH simulations explicitly
including a UV laser pulse of 6.43 eV photon energy reveals that after initial
excitation the population is almost equally spread over several close-lying
electronic states. This is followed by a fast nonradiative decay on the time
scale of 100-200 fs, with the final return to the ground state proceeding via
the S$_{1}$ state through the same types of CIs as observed in the field-free
simulations.
