High-resolution (λ/Δλ = 37,000) M band (4.7 μm) spectra are presented for the seven embedded infrared sources W3 IRS 5, S140 IRS 1, NGC 7538 IRS 1, NGC 7538 IRS 9, GL 2136, LkHα 101, and MWC 349A. Absorption lines of the fundamental vibrational band of 12CO are seen in all of the sources, and corresponding 13CO lines are detected in five. Other spectral features seen are (1) blueshifted 12CO absorption in five of the seven sources; (2) clear 12CO emission lines in two sources (S140 IRS 1 and NGC 7538 IRS 9), and possible CO emission lines in two others (W3 IRS 5 and NGC 7538 IRS 1); (3) hydrogen recombination lines in two sources (LkHα 101 and MWC 349A); (4) CO (υ = 1-2) absorption lines in one source, GL 2136; and (5) broad absorption at 2140 cm-1, due to solid CO, in W3 IRS 5, NGC 7538 IRS 1, and NGC 7538 IRS 9. Analysis of the CO lines yields values for the gas temperature and column density in the line of sight to each source. Results from the above seven objects are combined with our previously published results for W33A and GL 2591 to make a sample of nine objects. Although blueshifted CO absorption (i.e., outflowing gas) is seen in six of the nine objects, we discuss in this paper only the quiescent (i.e., nonoutflowing) gas. Cold gas is seen toward all sources, with temperature from 11 K (for MWC 349A) to 66 K (for W3 IRS 5). Eight of the nine sources show, in addition, hot gas, with temperature from 120 K (for W33A) to 1010 K (for GL 2591). The cold gas resides in the molecular cloud within which the objects are embedded. The gas temperatures of the cold component agree very well with temperatures deduced from emission lines at millimeter and centimeter wavelengths. For five of the lines of sight, 13CO column densities calculated from the infrared absorption lines are in quite good agreement with 13CO column densities calculated from radio emission lines, given the uncertainties inherent in the use of emission lines (e.g., beam dilution and self-absorption). The location of the hot gas component, and its heat source, is uncertain. We present arguments in favor of the view that the hot gas toward GL 2591, GL 2136, W3 IRS 5, and S140 IRS 1 is very near the embedded object and is heated via gas-grain collisions. For the sources NGC 7538 IRS 1, NGC 7538 IRS 9, LkHα 101, and W33A, the same model may apply, but the clumpy cloud picture presented by Harris et al. in 1987, in which ultraviolet photons from nearby hot stars penetrate and heat the gas, cannot be excluded. The ratio of solid to gaseous CO is obtained for seven sources, using solid CO abundances published by Sandford et al. in 1988. The fraction of CO in solid form is quite high for the sources NGC 7538 IRS 9 and W33A (4% and 10%, respectively). The four other lines of sight have less than 1% of CO in the solid state.
