  Type 2 quasars are luminous Active Galactic Nuclei whose central engines are
seen through large amounts of gas and dust. We present Spitzer spectra of
twelve type 2 quasars selected on the basis of their optical emission line
properties. Within this sample, we find a surprising diversity of spectra, from
those that are featureless to those showing strong PAH emission, deep silicate
absorption at 10 micron, hydrocarbon absorption, high-ionization emission lines
and H_2 rotational emission lines. About half of the objects in the sample are
likely Compton-thick, including the two with the deepest Si absorption. The
median star-formation luminosity of the objects in our sample measured from the
strength of the PAH features is 5x10^11 L_sun, much higher than for field
galaxies or for any other AGN sample, but similar to other samples of type 2
quasars. This suggests an evolutionary link between obscured quasars and peak
star formation activity in the host galaxy. Despite the high level of star
formation, the bolometric output is dominated by the quasar in all cases. For a
given strength of 10 micron Si absorption, ULIRGs are significantly colder than
are type 2 quasars (their F_nu[14.5 micron]/F_nu[27.5 micron] ratio is 0.5 dex
lower), perhaps reflecting different obscuration geometries in these sources.
We find that the appearance of the 10 micron feature (i.e., whether it shows in
emission or in absorption) is well-correlated with the optical classification
in type 1 and type 2 quasars, contrary to some models of clumpy obscuration.
Furthermore, this correlation is significantly stronger in quasars (L_bol>10^45
erg/s) than it is in Seyfert galaxies (L_bol<<10^45 erg/s).
