Optical-optical double resonance and Fourier transform spectroscopy: The Rb2 B 1Πu electronic state up to the quasibound energy levels

Nearly all quasibound vibrational energy levels of the Rb2 B 1Πu state were accessed via a double resonance excitation scheme. A resonant excitation process, X1Σg+ → A1Σu+ → (2)1Πg has been used to populate single ro-vibrational levels of the upper (2)1Πg state. Spectra of the (2)1Πg → B1Πu infrared fluorescence were recorded by high resolution Fourier transform spectroscopy. Taking account of previously studied B1Πu → X1Σg+ fluorescence spectra led to accurate effective molecular constant for the B1Πu state. The line broadening due to the tunneling effect was observed for the uppermost vibrational levels. The barrier height was found to be /2~ 205 cm−1 above its asymptotic limit (5S12 + 5P32) at 9.14Å.