Formation of $I2(B3Π)$ in the presence of $O2(a1Δ)$ Available to Purchase

The mechanism by which $I2(B3Π0)$ is excited in the chemical oxygen-iodine laser was studied by means of emission spectroscopy. Using the intensity of the $O2(b1Σ,υ′=0)→O2(X3Σ,υ″=0)$ band as a reference, $I2(B3Π0)$ relative number densities were assessed by measuring the $I2(B3Π0,υ′)→I2(X1Σ,υ″)$ emission intensities. Vibrationally excited singlet oxygen molecules $O2(a1Δ,υ′=1)$ were detected using infrared emission spectroscopy. The measured relative density of $O2(a1Δ,υ′=1)$ for the conditions of a typical oxygen-iodine laser medium amounted to $∼15%$ of the total $O2(a1Δ)$ content. Mechanisms for $I2(B3Π0)$ formation were proposed for both the $I2$ dissociation zone and the region downstream of the dissociation zone. Both pumping mechanisms involved electronically excited molecular iodine $I2(A′3Π2u,A3Π1u)$ as an intermediate. It is proposed that in the dissociation zone the molecular iodine $A′3Π2u$ and $A3Π1u$ states are populated in collisions with vibrationally excited singlet oxygen molecules $O2(a1Δ,υ′)$⁠, whereas in the downstream region of the dissociation zone those intermediate states are populated by the atomic iodine recombination process. $I2(B3Π0)$ is subsequently formed in collisions of $I2(A′3Π2u,A3Π1u)$ with singlet oxygen. We also demonstrated that $I2(B3Π0)$ does not participate measurably in the $I2$ dissociation process, and that energy transfer from $O2(b1Σ)$ does not excite $I2(B3Π0)$ to a significant degree.