Absorption spectra of the Cs2 molecule

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Abstract
The absorption spectra of the Cs2 molecule, over the wavelength range 0.8–1.3 μ, has been measured in pure Cs and a Cs–Ar mixture. The observed spectra, taken from 182 °C to 325 °C, were interpreted as both the allowed X1Σg+−A1Σu+ and the normally forbidden X1Σg+−a3πu transitions. Based on the classical Franck–Condon principle, the temperature dependence of the absorption of the X1Σg+–A1Σu+ transition for the wavelength range 0.9–1.21 μ was used to determine the potential energy curve for the A1Σu+ state. Also, the potential curve for the a3πu state was estimated. The bands of the X1Σg+–a3πu transition are blue‐shaded, indicating that the equilibrium internuclear separation of the a3πu is less than that of the X1Σg+; whereas, in the X1Σg+–A1Σu+ transition the bands are shaded to the red, indicating a greater equilibrium radius for the A1Σu+ state. Because of the short equilibrium radius of the a3πu state, the possibility exists that the a3πu and the x3Σu+ cross and that predissociation occurs. The implications of this on the possibility of the Cs2 molecule lasing at 1.13 or 1.19 μ are mentioned.