  Comet 21P/Giacobini-Zinner is a peculiar comet from the viewpoints of the
chemical and physical properties of its dust grains. We conduct optical
high-resolution spectroscopic observations of the comet. The intensity ratios
of forbidden oxygen lines (at 557.7, 630.0, and 636.4 nm) and ortho-to-para
abundance ratios (OPRs) of water cations (H$_2$O$^+$) and amidogen radicals
(NH$_2$) are obtained while only the upper limit for $^{14}$N/$^{15}$N in the
amidogen radical is restricted. The OPRs of H$_2$O$^+$ and NH$_2$ are similar
to those of other comets, although the real meaning of these OPRs is still
debated. Based on the observation of the forbidden emission lines of oxygen
atoms, it can be concluded that the comet is depleted in CO$_2$. In
consideration with the depletion in other highly volatile species found in the
near-infrared region and the presence of complex organics in comet
21P/Giacobini-Zinner, this comet might form in a warmer region in the solar
nebula compared with other comets.
