Direct observation of the D′ 2 g( 3P2)– A′ 3Π(2 u) system for Cl 2 by laser induced fluorescence spectroscopy: Determination of the absolute position of the A′ state

Abstract

In a discharged supersonic jet of Cl 2, transitions of the D′ 2 g ( 3 P 2)– A′ 3Π(2 u ) system for 35Cl 2 were observed directly by laser induced fluorescence spectroscopy. By a discharge in Cl 2, the Cl 2 molecules were populated into the A′ state, which is a metastable and optically forbidden state, from the X 1 Σ g + ( 0 g + ) state. An ultraviolet laser radiation excites the molecules to the D′ ion-pair state. A set of Dunham parameters for the A′ state is determined from a global least-squares fitting for 59 vibronic bands with v″ = 0–7. In the fitting, the previously reported data, T( v) and B( v) for the v = 14 and 15 bands of the A′ state [T. Ishiwata, A. Ishiguro, K. Obi, J. Mol. Spectrosc. 147 (1991) 300–320], were included. Y 00 = 57295.723(5) cm −1 of the D′ state [J.-H. Si, T. Ishiwata, K. Obi, J. Mol. Spectrosc. 147 (1991) 334–345] was also included in the global fitting in order to determine the absolute position of the A′ state. The determined parameters of the A′ state are Y 00 = 17171.506(14), Y 10 = 255.915(85), Y 20 = −4.465(70), Y 30 = −8.7(23) × 10 −2, Y 40 = 6.3(35) × 10 −3, Y 50 = −4.9(26) × 10 −4, Y 60 = 1.43(69) × 10 −5, Y 01 = 0.16282(15), Y 11 = −2.363(68) × 10 −3, Y 21 = −5.01(93) × 10 −5, and Y 31 = −3.01(36) × 10 −6 (in cm −1 and one standard deviations of the fit in parentheses). The absolute position of the A′ state is determined with good accuracy.