Isotope shift in optical spectra of MoO

Abstract Four absorption bands of the jet-cooled molybdenum monoxide (MoO) molecule involving seven natural Mo isotopes have been investigated using laser induced fluorescence spectroscopy. All bands have large isotope shifts in rotational resolution, and are assigned to the transitions from the ground X 5Π−1 (v′′ = 0) state to the upper [14.11]2, [14.15]2, [14.24]2 and [15.04]2 states, respectively. The accurate rotational constants of seven isotopologues in the ground and excited states are obtained. In addition, the vibrational constants of the ground electronic state are obtained by the isotopically resolved single-vibrational-level emission spectra. The isotope effect in the rovibronic structure of the ground electronic state follows the rigid rotor model and harmonic oscillator model. Strong homogeneous perturbations in the upper states are found resulting in unexpected Franck-Condon factors and irregular dependences of the vibrational isotope shifts and bond lengths with reduced mass.