ABSTRACT
The rotationally resolved magnetic dipole absorption spectrum of the oxygen A-band b(1)Σ(g)(+)(v=0) <- X(3)Σ(g)(-)(v=0) perturbed by collisions with helium was studied theoretically using the impact approximation. To calculate the relaxation matrix, scattering calculations were performed on a newly computed helium-oxygen (b(1)Σ(g)(+)) interaction potential as well as on a helium-oxygen (X(3)Σ(g)(-)) interaction potential from the literature. The calculated integrated line cross sections and broadening coefficients are in good agreement with experimental results from the literature. Additionally, cavity ring-down experiments were performed in the wings of the spectral lines for a quantitative study of line-mixing, i.e., the redistribution of rotational line intensities by helium-oxygen collisions. It is shown that inclusion of line-mixing in the theory is required to reproduce the experimentally determined absolute absorption strengths as a function of the density of the helium gas.
ABSTRACT
Using cavity ring-down spectroscopy we measured the collision induced absorption spectrum associated with the a(1)Δ(v = 2) âX(3)Σ(g)(-)(v = 0) band of oxygen near 922 nm both in pure oxygen and in mixtures of oxygen and nitrogen. For pure oxygen, we report for this band an integrated absorption of (1.56 - 0.04/+0.40) × 10(-5) cm(-2) amg(-2). We find that collisions between oxygen and nitrogen do not result in any measurable CIA signal. At 1 bar of oxygen, this collision induced transition is much stronger than the allowed magnetic dipole and electric quadrupole transitions.
ABSTRACT
We have determined the collision-induced absorption (CIA) spectrum in the O(2) B-band in pure oxygen. We present absolute extinction coefficients of the minimums in between rotational lines using cavity ring-down spectroscopy. The measured extinction is corrected for the B-band magnetic dipole absorption using a model which includes line-mixing. The remaining extinction consists of collision-induced absorption and Rayleigh scattering. We retrieve the magnitude of the Rayleigh scattering and the CIA spectrum based on their individual different behavior with density. The CIA spectrum of the B-band resembles that of the oxygen A-band in shape but not in magnitude. The contribution of CIA to the total B-band absorption is 40% higher in comparison to that of the A-band.
ABSTRACT
This paper reports on the absorption of molecular oxygen in the region of 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. Absolute binary absorption coefficients in minima between absorption lines of the A-band spectrum have been measured and tabulated. We use the so-called adjustable branch coupling model including line mixing to calculate the magnetic dipole absorption in order to determine the contribution of collision induced absorption. The line mixing model has been optimized such that the collision induced absorption spectrum is smooth.
