High resolution laser spectroscopy of the <i>c</i> 3Σ+←<i>X</i> 1Σ+ and <i>b</i> 3Π←<i>X</i> 1Σ+ forbidden transitions in NaK

Abstract

The ‘‘spin-forbidden’’ c 3Σ+←X 1Σ+ and b 3Π←X 1Σ+ band systems have been studied in the excitation spectrum of the 23Na39K molecule in the range of 560–600 nm. Single mode continuous wave (cw) dye laser excitation in a supersonic molecular beam yielded Doppler-free spectra and allowed resolution of the hyperfine structure of lines. Mutual perturbations of the c 3Σ+, b 3Π, and B 1Π states were studied. The observed vibrational variation of perturbation matrix elements for c 3Σ+–B 1Π interaction was used to assign the absolute vibrational numbering in the c state. The deperturbed molecular constants of this state have been found and its fine structure examined. The hyperfine structure in the c 3Σ+ and b 3Π states was studied for several vibrational levels and through a wide range of J values. For the c 3Σ+ state, fits of known theoretical expressions for the hyperfine energies to the experimental data provided accurate values of the hyperfine coupling constants. The results are discussed in terms of the electronic structure of the c 3Σ+ state.