Absorption spectra of the Cs2 molecule

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 X¹Σ_g⁺−A¹Σ_u⁺ and the normally forbidden X¹Σ_g⁺−a³π_u transitions. Based on the classical Franck–Condon principle, the temperature dependence of the absorption of the X¹Σ_g⁺–A¹Σ_u⁺ transition for the wavelength range 0.9–1.21 μ was used to determine the potential energy curve for the A¹Σ_u⁺ state. Also, the potential curve for the a³π_u state was estimated. The bands of the X¹Σ_g⁺–a³π_u transition are blue‐shaded, indicating that the equilibrium internuclear separation of the a³π_u is less than that of the X¹Σ_g⁺; whereas, in the X¹Σ_g⁺–A¹Σ_u⁺ transition the bands are shaded to the red, indicating a greater equilibrium radius for the A¹Σ_u⁺ state. Because of the short equilibrium radius of the a³π_u state, the possibility exists that the a³π_u and the x³Σ_u⁺ 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.