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International audience; This paper reports on the effect of collisions between nitrogen and oxygen on absorption in the A-band near 760 nm under atmospheric conditions relevant for satellite retrieval studies. We use pulsed laser cavity ring-down spectroscopy with a narrow bandwidth laser and use pressure scans to increase the accuracy of the measured oxygen extinction coefficients. We use the so-called Adjustable Branch Coupling model to describe line mixing in the magnetic allowed A-Band dipole absorption and we retrieve the collision induced absorption spectrum due to N$_2$-O$_2$ collisions.

The first fully allowed spectroscopic transition in O2 is the transition comprising the well-known Schumann–Runge bands and continuum. We report a velocity-map imaging study in which the O(1 D) angular momentum polarisation and O(3 P) spin–orbit branching ratios arising from this process have been measured. We show that direct 157 nm excitation into the Schumann–Runge continuum leads to extremely strong angular momentum polarisation in the O(1D) product. Comparison with previous studies indicates that this is a general feature of dissociation via the B state. The fine structure branching ratios in the co-fragment O(3P J=2,1,0) were measured to be 88.5 ± 1.6 : 9.7 ± 1.4 : 1.9 ± 0.4. Based on a consideration of the Massey parameter for the system, the data were modelled using theoretical calculations based on adiabatic and diabatic models of the dissociation. While both models were able to describe some aspects of the dissociation accurately, neither was able to predict both the fine structure branching rat...