Structure and rovibrational analysis of the [O2(1Δg)v=0]2←[O2(3Σg−)v=0]2 transition of the O2 dimer

Abstract

The rotationally resolved absorption spectrum of the ${\mathrm{O}}_{\mathrm{2}}$ dimer involving the $[{\mathrm{O}}_{\mathrm{2}}{(}^1{\Delta }_g{)}_{\text{v=0}}{]}_2\mathrm{\leftarrow [}{\mathrm{O}}_{\mathrm{2}}{(}^3{\Sigma }_g^{-}{)}_{\text{v=0}}{]}_2$ transition has been recorded near 632.6 nm by continuous wave Cavity Ring Down Spectroscopy in a supersonic slit jet expansion of pure ${\mathrm{O}}_{\mathrm{2}}.$ A quadratic dependence of the absorption in the jet versus the stagnation pressure is observed. A rotational temperature of 12 K is derived from the $({\mathrm{O}}_{\mathrm{2}}{)}_2$ rotational analysis. The high spectral resolution of the CW-CRDS measurements limited by the residual Doppler broadening in the jet and the low rotational temperature allow the first rotational analysis in this open-shell complex. The same spectrum was also recorded by Intracavity Laser Absorption Spectroscopy and the comparison of the performances of the two methods is discussed. Among more than 600 lines measured between 15 800 and $\text{15\hspace{0.05em}860\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{-1}}$ from the CW-CRDS spectrum, 40 were assigned to the ${}^R{P}_0,$ ${}^R{Q}_0,$ and ${}^R{R}_0$ branches of two subbands associated with $B_1^{-}{\mathrm{\leftarrow A}}_1^{+}$ and $A_1^{+}{\mathrm{\leftarrow B}}_1^{-}$ transitions between the ground and excited rovibrational levels, labeled following the ${\mathrm{G}}_{\mathrm{16}}$ permutation inversion representation. Forty five lines were assigned to ${}^P{P}_2,$ ${}^P{Q}_2,$ and ${}^P{R}_2$ branches of two subbands associated with $B_1^{-}{\mathrm{\leftarrow A}}_1^{+}$ and $A_1^{+}{\mathrm{\leftarrow B}}_1^{-}$ transitions. The subbands centered at 15 808.401(49) ${\mathrm{[A}}_1^{+}{\mathrm{\leftarrow B}}_1^{-}]$ and $\text{15\hspace{0.05em}813.134(37)\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{-1}}$ ${\mathrm{[B}}_1^{-}{\mathrm{\leftarrow A}}_1^{+}]$ for those arising from $\text{K=0,}$ and at 15 812.656(20) ${\mathrm{[A}}_1^{+}{\mathrm{\leftarrow B}}_1^{-}]$ and 15 818.277(35) ${\mathrm{[B}}_1^{-}{\mathrm{\leftarrow A}}_1^{+}]$ when arising from $\text{K=2,}$ are analyzed considering $({\mathrm{O}}_{\mathrm{2}}{)}_2$ as a slightly asymmetric prolate top. The rotational analysis of the two...