Doppler-free polarization spectroscopy of the B 1Πu –X 1Σ+g band system of K2

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Abstract
The B 1Πu–X 1Σ+g band system of the K2 molecule is investigated by Doppler‐free polarization spectroscopy in a heat pipe oven. The transitions are measured in the region of 615 to 660 nm including vibrational levels up to v″=17 in the X state and all vibrational levels of the B state up to the dissociation limit. A Fabry–Perot interferometer is calibrated using metastable neon and K2 secondary wavelength standards to provide absolute accuracy in the frequency determination of less than 20 MHz. The comprehensive study of the band system is completed by LIF measurements to determine vibrational levels of the ground state up to v‘=62. A detailed analysis has been completed and the coefficients are given in a Dunham expansion that accurately represents the frequencies of lines with specified vibrational and rotational quantum numbers. The B and X potential curves and the Franck–Condon factors for the transitions between B and X states are determined. The dissociation energies have been found to be 4447±15 cm−1 for the X state and 2113±15 cm−1 for the B state. The height of the potential barrier of the B state above the 4 2P3/2+4 2S1/2 atomic levels is 295±17 cm−1 at an internuclear distance of 8.1±0.1 Å.