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Experimental verification of the Einstein A-coefficient used for evaluation of O2(g) concentration in the chemical oxygen-iodine laser

This paper is a contribution to the current discussion on the Einstein coefficient for spontaneous emission (A-coefficient) of singlet delta oxygen, O2(g), that is often used for an evaluation of O2(g) concentration in a chemical oxygen-iodine laser (COIL). The published values of the A-coefficient vary in a wide range, corresponding to a radiative lifetime of O2(g), , from ~53 to ~151 min. This could make an evaluation of COIL operation questionable. In this paper, the Einstein A-coefficient is estimated, based on the comparison of O2(g) concentrations determined by two independent methods: electron paramagnetic resonance and emission spectroscopy. Within the accuracy of the experimental techniques used, the value of the A-coefficient resulting from our investigation is (2.24±0.40) × 10-4 s-1, corresponding to of ~74 min. This result is more consistent with the value of 2.58 × 10-4 s-1 of Badger et al [1] than with the value of 1.47 × 10-4 s-1 reported recently by Mlynczak and Nesbitt [2], who raised doubt about the Badger et al value.