iSHELL M2 spectra (RP ﹩\equiv ﹩ λ/Δλ ﹩\cong ﹩ 4.5 × 10⁴) of CO and H₂O in Comet 13P and two other OCCs that together have very different abundance ratios CO/H₂O as detailed in Section 3.1, representing signal contained in a 0﹩\mathop{.}\limits^{\unicode{x02033}}﹩75 × 2﹩\mathop{.}\limits^{\unicode{x02033}}﹩5 aperture centered on the nucleus (nucleus-centered spectra; Section 4.1). (a). Four orders encompassing the strongest CO lines and showing substantial enrichment in 13P, with 18 of 19 CO lines included in our analysis (only P1 was excluded owing to insufficient transmittance and accordingly is labeled “x”). (b–d). Single-order spectra, with telluric absorptions spectrally aligned, thereby showing the differing geocentric Doppler shifts (in parentheses) and disparate CO abundances in these three comets. Line-by-line nucleus-centered production rates for CO and H₂O in Comet 13P are listed in Table 2.