Eur. Phys. J. D 46, 241-249 (2008)
https://doi.org/10.1140/epjd/e2007-00307-2

Spectroscopy of the a³Σ_u⁺ state and the coupling to the X¹Σ_g⁺ state of K₂^*

¹ Department of Physics, Sofia University, 5 James Bourchier boulevard, 1164 Sofia, Bulgaria
² Department of Physics, Technical University of Varna, ul. Studentska 2, 9010 Varna, Bulgaria
³ Institut für Quantenoptik, Leibniz Universität Hannover, Welfengarten 1, 30167 Hannover, Germany

Corresponding author: ^a tiemann@iqo.uni-hannover.de

Received: 8 August 2007
Revised: 4 October 2007
Published online: 14 November 2007

Abstract

We report on high resolution Fourier-transform spectroscopy of fluorescence to the a³Σ_u⁺ state induced by two-photon or two-step excitation from the X¹Σ_g⁺ state to the 2³Π_g state in the molecule K₂. These spectroscopic data are combined with recent results of Feshbach resonances and two-color photoassociation spectra for deriving the potential curves of X¹Σ_g⁺ and a³Σ_u⁺ up to the asymptote. The precise relative position of the triplet levels with respect to the singlet levels was achieved by including the excitation energies from the X¹Σ_g⁺ state to the 2³Π_g state and the frequencies of the fluorescence down to the a³Σ_u⁺ state in the simultaneous fit of both potentials. The derived precise potential curves allow for reliable modeling of cold collisions of pairs of potassium atoms in their ²S ground state.