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

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 5800-7700 cm(-1) are assigned to the transitions A(3)Pi (A(2)0(+)) -> X-3 Sigma(-)(X(1)0(+), X(2)1). Nine bands of the A(2)0(+) -> X(1)0(+) and three bands of the A(2)0(+) -> X(2)1 system were measured at high spectral resolution and rotationally analysed. The rotational and vibrational analyses yielded the spectroscopic parameters of the X(1)0(+), X(2)1, and A(2)0(+) states. For KSb, in the range of the sensitive Ge detector, only one sequence of bands was measured near 6880 cm(-1). By analogy with the previously observed spectra of NaSb and NaAs these bands were identified to be the Delta v = 0 sequence of the a2 -> X(2)1 transition of KSb. Some very weak bands observed at low resolution in the range 3800-5200 cm(-1) are assigned to the transitions A(3)Pi(A(2)1)-> X-3 Sigma(-)(X(1)0(+), X(2)1). 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. (C) 2017 Elsevier Inc. All rights reserved.