  The eruption of Nova V2891 Cygni in 2019 offers a rare opportunity to explore
the shock-induced processes in novae ejecta. The spectral evolution shows
noticeable differences in the evolution of various oxygen emission lines such
as O I 7773 {\AA}, O I 8446 {\AA}, O I 1.1286 $\mu$m, O I 1.3164 $\mu$m, etc.
Here, we use spectral synthesis code CLOUDY to study the temporal evolution of
these oxygen emission lines. Our photoionization model requires the
introduction of a component with a very high density ($n ~ 10^{11}$ cm$^{-3}$)
and an enhanced oxygen abundance (O/H $\sim$ 28) to produce the O I 7773 {\AA}
emission line, suggesting a stratification of material with high oxygen
abundance within the ejecta. An important outcome is the behaviour of the O I
1.3164 $\mu$m line, which could only be generated by invoking the collisional
ionization models in CLOUDY. Our phenomenological analysis suggests that O I
1.3164 $\mu$m emission originates from a thin, dense shell characterized by a
high density of about $10^{12.5} - 10^{12.8}$ cm$^{-3}$, which is most likely
formed due to the strong internal collisions. If such is the case, the O I
1.3164 $\mu$m emission presents itself as a tracer of shock-induced dust
formation in V2891 Cyg. The collisional ionization models have also been
successful in creating the high-temperature conditions ($~ 7.07 - 7.49 \times
10^5$ K) required to reproduce the observed high ionization potential coronal
lines, which coincide with the epoch of dust formation and evolution of the O I
1.3164 $\mu$m emission line.
