Direct observation of the D′ 2g(3P2)-A′ 3Π(2u) system for Cl2 by laser induced fluorescence spectroscopy: Determination of the absolute position of the A′ state

In a discharged supersonic jet of Cl2, transitions of the D′ 2g(3P2)-A′ 3Π(2u) system for 35Cl2 were observed directly by laser induced fluorescence spectroscopy. By a discharge in Cl2, the Cl2 molecules were populated into the A′ state, which is a metastable and optically forbidden state, from the X1Σg+(0g+) 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. Y00 = 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 Y00 = 17171.506(14), Y10 = 255.915(85), Y20 = −4.465(70), Y30 = −8.7(23) × 10−2, Y40 = 6.3(35) × 10−3, Y50 = −4.9(26) × 10−4, Y60 = 1.43(69) × 10−5, Y01 = 0.16282(15), Y11 = −2.363(68) × 10−3, Y21 = −5.01(93) × 10−5, and Y31 = −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.