Carbon monoxide emissions at 4.7μm from Venus’ atmosphere

In January 1987, high-resolution spectra of the dayside of Venus in the 2080–2185cm-1 range, recorded with the Canada–France–Hawaii telescope using a Fourier-transform spectrometer, revealed two sequences of narrow emission lines, corresponding to the v=(1–0)v=(1–0) and v=(2–1v=(2–1) vibrational bands of carbon monoxide. Higher-quality spectra of Venus were recorded subsequently (September 1994) on several points on Venus. We present here the Venus observations and the associated intensities and rotational temperatures. Possible mechanisms responsible for these emissions are reviewed. We show that (1) fluorescence following infrared solar excitation and (2) CO2CO2 photolysis leading to the creation of vibrationally excited CO are two plausible mechanisms. A quantitative model which takes into account these two processes, collisions and radiative trapping is presented and allows an approximate matching of the observed line intensities. Inferred temperatures are 170–220 K for the (2–1) band, probing the 100–110 km range, and 220–300 K for the (1–0) band (125–145 km altitude).