ABSTRACT
Collision-induced absorption between O2 and CO2 molecules associated with the a1Δg (v = 1) â X3Σ-g (v = 0) band of oxygen around 1060 nm was measured using cavity ring-down spectroscopy. The lineshape for this transition is measured for the first time, and the integrated cross-section is found to be smaller than the only previous report. For pure oxygen, we find an integrated absorption value of (2.10 ± 0.31) × 10-4 cm-2 amg-2 which is in good agreement with the previous reported values. For O2-CO2 collisions we report an integrated value of (6.37 ± 1.09) × 10-5 cm-2 amg-2 which is small but still significant and not accounted for by theory.
ABSTRACT
In the version of this Article originally published, Figures 3 and 4 were erroneously swapped, this has been corrected in all versions of the Article.
ABSTRACT
Collision-induced absorption is the phenomenon in which interactions between colliding molecules lead to absorption of light, even for transitions that are forbidden for the isolated molecules. Collision-induced absorption contributes to the atmospheric heat balance and is important for the electronic excitations of O2 that are used for remote sensing. Here, we present a theoretical study of five vibronic transitions in O2-O2 and O2-N2, using analytical models and numerical quantum scattering calculations. We unambiguously identify the underlying absorption mechanism, which is shown to depend explicitly on the collision partner-contrary to textbook knowledge. This explains experimentally observed qualitative differences between O2-O2 and O2-N2 collisions in the overall intensity, line shape and vibrational dependence of the absorption spectrum. It is shown that these results can be used to discriminate between conflicting experimental data and even to identify unphysical results, thus impacting future experimental studies and atmospheric applications.
