The (3) 1Π–(3) 1Σ+ system of KRb

Infrared fluorescence of the KRb molecule in the spectral range 6500–8000 cm−1, arising when the levels of the (3) 1Π state are excited by the 457.9, 465.8, 472.7, and 476.5 nm lines of an argon-ion laser, has been recorded by Fourier transform spectrometry. A part of the fluorescence is assigned to the system (3) 1Π→(3) 1Σ+. The (3) 1Σ+ state energy levels up to v=15 have been determined. The main spectroscopic constants for this state are Te=13995.465 (10) cm−1, ωe=40.76310 (40) cm−1, ωexe=−0.26988 (71)×10−1 cm−1, Be=22.8215 (28)×10−3 cm−1, Re=4.17125 Å. The unusual spacing of the vibrational levels reflects the ionic character of the state. Preliminary values for the strongly perturbed (3) 1Π state are Te=21762.0, ωe=41.36, ωexe=0.184, Be=28.82×10−3 cm−1.