Electronic and vibrational spectroscopy of the low-lying states of potassium mono-sulphide KS, and comparison in the series of MS (M = Li, Na, K, Rb, Cs)

ABSTRACT

Potential energy curves (PECs) of the lowest electronic states of the potassium mono-sulphide KS have been determined with highly correlated ab initio calculations, using internally contracted multi reference interaction configuration methods including Davidson correction (MRCI + Q) with and without considering spin-orbit effects. For the three low-lying bound states, we report a set of spectroscopic parameters including equilibrium distances, dissociation energies, vibrational and rotational constants. The effects of spin-orbit-induced changes on these parameters are also discussed. An analysis of the properties of the three bound states, X²Π, 1²Σ⁺ and 2²Π, illustrates the common characteristics of the whole series of compounds in the MS family (M = Li, Na, K, Rb, Cs). Indeed, the shapes of the PECs of these bound states are strongly affected by the interactions between the two ionic states, ²Σ⁺ and ²Π, correlating at large internuclear separations (R_MS) to the first ionic dissociation limit [M⁺ + S⁻] and the electronic states correlating to the three/four lowest dissociation limits. The spectroscopy of these low-lying electronic states and the lifetime of their vibrational levels are thus affected by the spin-orbit interactions which are mainly related to the S atom and consequently common to all alkali-metal mono-sulphides.

GRAPHICAL ABSTRACT

KEYWORDS:

• Electronic states
• spin-orbit effect
• potential curves
• spectroscopy

Acknowledgments

We gratefully acknowledge the support of the COST Action CM1405 entitled MOLIM: Molecules in Motion.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Gilberte Chambaud http://orcid.org/0000-0002-8031-2746

Majdi Hochlaf http://orcid.org/0000-0002-4737-7978