L-band spectra of V838 Mon. The solid gray lines represent individual calibrated spectra for both nights. The red line is a weighted-mean average spectrum, with error bars representing one standard deviation in individual spectra. The bottom panel shows opacity curves for four species. They are arbitrarily scaled. All simulations were smoothed to match the resolution of the observations. SiO and H₂O curves weresimulated for circumstellar gas temperatures, while SH and OH were assumed to form in photospheric temperatures. The latter two are unlikely to be present in the spectrum of V838 Mon.