Theoretically predicted CO2 lines near 700 nm not observed

Abstract

We present an experimental study of carbon dioxide absorption in the transparency window near 700 nm, where different calculations predicted several extremely weak bands. The measurements were done using the optical frequency comb-assisted cavity ring-down spectrometer reaching sensitivity (noise-equivalent absorption) of 3.1⋅10−12 cm−1. None of 21 lines, predicted by the most comprehensive calculations, were detected in five separate spectral regions near 700 nm. Our estimated detection limit ranges between 3 and 21 times lower than the expected peak absorption in the conditions of the experiment.