The (3)(1)Pi-(3)(1)Sigma(+) system of KRb

Infrared fluorescence of the KRb molecule in the spectral range 6500-8000 c m(-1), arising when the levels of the (3) (1)Pi state are excited by the 45 7.9, 465.8, 472.7, and 476.5 nm lines of an argon-ion laser, has been recor ded by Fourier transform spectrometry. A part of the fluorescence is assign ed to the system (3) (1)Pi --> (3) (1)Sigma(+). The (3) (1)Sigma(+) state e nergy levels up to v = 15 have been determined. The main spectroscopic cons tants for this state are T-e = 13995.465(10) cm(-1) omega(e)= 40.76310(40) cm(-1), omega(e)x(e) = -0.26988(71) x 10(-1) cm(-1), B-e = 22.8215 (28) x 1 0(-3) cm(-1), R-e = 4.17125 Angstrom. The unusual spacing of the vibrationa l levels reflects the ionic character of the state. Preliminary values for the strongly perturbed (3) (1)Pi state are T-e = 21762.0, omega(e) = 41.36, omega(e)x(e) = 0.184, B-e = 28.82 x 10(-3) cm(-1). (C) 1999 Elsevier Scien ce B.V. All rights reserved.