Infrared emission spectroscopy of the a′3Σ+ -a3Π band of CS

Abstract The infrared emission spectrum of the CS a ′ 3 Σ + - a 3 Π transition has been observed with a FT spectrometer in the 1800–10,500 cm −1 region. Thirteen bands were analyzed to obtain molecular constants in 4 (v = 0–3) vibrational states of a 3 Π and 7 (v = 0–6) vibrational states of a ′ 3 Σ + , where the effects of perturbations from nearby states were taken into account directly by using an energy matrix that includes off-diagonal spin-orbit and rotational interactions. Due to the large spin-orbit interaction, inclusion of higher-order terms of the perturbation was necessary for the fitting. The vibrational energies of v = 0–5 in a′ 3 Σ + have been determined experimentally for the first time, and a simultaneous analysis with the previous data of v = 7–22 gives T e0  = 30689.40(40), ω e  = 830.680(87), ω e x e  = 5.0372(38) cm −1 for a ′ 3 Σ + , with one standard deviation in parentheses.