  The nearby spiral galaxy NGC 7331 was spectrally mapped from 5-38um using all
modules of Spitzer's IRS spectrograph. A strong new dust emission feature,
presumed due to PAHs, was discovered at 17.1um. The feature's intensity is
nearly half that of the ubiquitous 11.3um band. The 7-14um spectral maps
revealed significant variation in the 7.7 and 11.3um PAH features between the
stellar ring and nucleus. Weak [OIV] 25.9um line emission was found to be
centrally concentrated in the nucleus, with an observed strength over 10% of
the combined neon line flux, indicating an AGN or unusually active massive star
photo-ionization. Two [SIII] lines fix the characteristic electron density in
the HII regions at n_e < ~200 cm^-3. Three detected H_2 rotational lines,
tracing warm molecular gas, together with the observed IR continuum, are
difficult to match with standard PDR models. Either additional PDR heating or
shocks are required to simultaneously match lines and continuum.
