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Nova Mon 2012 was the first classical nova to be detected as a high energy$\gamma$-ray transient, by Fermi-LAT, before its optical discovery. We study atime sequence of high resolution optical echelle spectra (Nordic OpticalTelescope) and contemporaneous NOT, STIS UV, and CHIRON echelle spectra (Nov20/21/22). We use [O III] and H$\beta$ line fluxs to constrain the propertiesof the ejecta. We derive the structure from the optical and UV line profilesand compare our measured line fluxes for with predictions using Cloudy withabundances from other ONe novae. Mon 2012 is confirmed as an ONe nova. We findE(B-V)=0.85$\pm$0.05 and hydrogen column density $\approx 5\times 10^{21}$cm$^{-2}$. The corrected continuum luminosity is nearly the same in the entireobserved energy range as V1974 Cyg, V382 Mon, and Nova LMC 2000 at the sameepoch after outburst. The distance, about 3.6 kpc, is quite similar to V1974Cyg. The line profiles can be modeled using an axisymmetric bipolar geometryfor the ejecta with various inclinations of the axis to the line of sight, 60\le i \le 80 degrees, an opening angle of \approx$70 deg, inner radius $\DeltaR/R(t)\approx 0.4$ for permitted lines and less filled for forbidden lines. Thefilling factor $f\approx 0.1-0.3$ implying M(ejecta) $\leq 6\times10^{-5}$M$_\odot$. The ONe novae appear to comprise a single physical classwith bipolar high mass ejecta, similarly enhanced abundances, and a commonspectroscopic evolution within a narrow range of luminosities. The detected$\gamma$-ray emission may be a generic phenomenon, common to all ONe novae,possibly to all classical novae, and connected with acceleration and emissionprocesses within the ejecta (abstract severely truncated).

The spectroscopic evolution of the $\gamma$-ray emitting classical nova Nova Mon 2012. I. Implications for the ONe subclass of classical novae