Theoretical and experimental study of the electronic states and spectra of KBi and KSb

Abstract

Gas phase emission spectra of the hitherto unknown free radicals KBi and KSb were measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which bismuth or antimony vapor in argon carrier gas was passed through a microwave discharge and mixed with potassium vapor in an observation tube. For KBi, two systems of blue-degraded bands observed in the range 5800–7700cm−1 are assigned to the transitions A3Π (A20+)→X3Σ−(X10+, X21). Nine bands of the A20+→X10+ and three bands of the A20+→X21 system were measured at high spectral resolution and rotationally analysed. The rotational and vibrational analyses yielded the spectroscopic parameters of the X10+, X21, and A20+ states. For KSb, in the range of the sensitive Ge detector, only one sequence of bands was measured near 6880cm−1. By analogy with the previously observed spectra of NaSb and NaAs these bands were identified to be the Δv=0 sequence of the a2→X21 transition of KSb. Some very weak bands observed at low resolution in the range 3800–5200cm−1 are assigned to the transitions A3Π (A21)→X3Σ −(X10+, X21).To aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential energy curves for the low-lying states of KBi and KSb, vibrational constants, equilibrium internuclear distances, and also electric dipole transition moments connecting the states.