Optical-optical double resonance and Fourier transform spectroscopy: the Rb-2 B-1 Pi(u) electronic state up to the quasibound energy levels

Nearly all quasibound vibrational energy levels of the Rb-2 B-1 Pi(u) state were accessed via a double resonance excitation scheme. A resonant excitation process, X-1 Sigma(g)(+) --> A(1) Sigma(u)(+) --> (2)(1) Pi(g) has been used to populate single re-vibrational levels of the upper (2)(1) Pi(g) state. Spectra of the (2)(1) Pi(g) --> B-1 Pi(u) infrared fluorescence were recorded by high resolution Fourier transform spectroscopy. Taking account of previously studied B-1 Pi(u) --> X-1 Sigma(g)(+)+ fluorescence spectra led to accurate effective molecular constants for the B-1 Pi(u) state. The line broadening due to the tunneling effect was observed for the uppermost vibrational levels. The barrier height was found to be approximate to 205 cm-l above its asymptotic limit (5S(1/2) + 5P(3/2)) at 9.14 Angstrom. (C) 1997 Elsevier Science B.V.