  We simulate the photodynamics of gas-phase cyclobutanone excited to the S$_2$
state using fewest switches surface hopping (FSSH) dynamics powered by
time-dependent density functional theory (TDDFT). We predict a total C3+C2
photoproduct yield of 9%, with a C3:C2 product ratio of 1:8. Two primary
S$_2$$\rightarrow$S$_1$ conical intersections are identified: $\beta$ stretch
and CCH bend, with the higher energy $\beta$ stretch being associated with
sub-picosecond S$_2$ decay. Excited state lifetimes computed with respect to
electronic state populations were found to be 7.0 ps (S$_2$$\rightarrow$S$_1$)
and 550 fs (S$_1$$\rightarrow$S$_0$). We also generate time-resolved difference
pair distribution functions ($\Delta$PDFs) from our TDDFT-FSSH dynamics results
in order to generate direct comparisons to ultrafast electron diffraction
experiment observables. Global and target analysis of time-resolved
$\Delta$PDFs produced a distinct set of lifetimes: i) a 0.462 ps decay, and ii)
a 16.8 ps decay that both resemble the S$_2$ minimum, as well as iii) a long
($>$ nanosecond) decay that resembles the S$_1$ minimum geometry and the fully
separated C3/C2 products. Finally, we contextualize our results by considering
the impact of the most likely sources of significant errors.
