  A new synchrotron study for CH$_2$F$_2$ from has been combined with earlier
data. The onset of absorption, band I and also band IV, is resolved into broad
vibrational peaks, which contrast with the continuous absorption previously
claimed. A new theoretical analysis, using a combination of time dependent
density functional theory (TDDFT) calculations and complete active space
self-consistent field, leads to a major new interpretation. Adiabatic
excitation energies (AEEs) and vertical excitation energies, evaluated by these
methods, are used to interpret the spectra in unprecedented detail using
theoretical vibronic analysis. This includes both Franck-Condon (FC) and
Herzberg-Teller (HT) effects on cold and hot bands. These results lead to the
re-assignment of several known excited states and the identification of new
ones. The lowest calculated AEE sequence for singlet states is 1$^1$B$_1$
$\sim$ 1$^1$A$_2$ < 2$^1$B$_1$ < 1$^1$A$_1$ < 2$^1$A$_1$ < 1$^1$B$_2$ <
3$^1$A$_1$ < 3$^1$B$_1$. These, together with calculated higher energy states,
give a satisfactory account of the principal maxima observed in the VUV
spectrum. Basis sets up to quadruple zeta valence with extensive polarization
are used. The diffuse functions within this type of basis generate both valence
and low-lying Rydberg excited states. The optimum position for the site of
further diffuse functions in the calculations of Rydberg states is shown to lie
on the H-atoms. The routine choice on the F-atoms is shown to be inadequate for
both CHF$_3$ and CH$_2$F$_2$. The lowest excitation energy region has mixed
valence and Rydberg character. TDDFT calculations show that the unusual
structure of the onset arises from the near degeneracy of 1$^1$B$_1$ and
1$^1$A$_2$ valence states, which mix in symmetric and antisymmetric
combinations.
