  We have developed a dispersive spectrometer using a compact immersion grating
for direct frequency comb spectroscopy in the long-wave infrared region of 8-10
{\mu}m. A frequency resolution of 463 MHz is achieved, which is the highest
reported in this wavelength region with a dispersive direct frequency comb
spectrometer. We also demonstrate individual mode-resolved imaging of the
frequency comb spectrum by Vernier cavity filtering and apply this to obtain
both simple and complex molecular spectra. These results indicate that the
immersion grating spectrometer offers the next advancement for sensitive,
high-resolution spectroscopy of transient and large/complex molecules when
combined with cavity enhancement and cooling techniques.
