Quasibound levels and shape resonances of 39K2(B 1Πu) crossed laser-molecular beam studies and analytical interpretation

Abstract

Quasibound levels and shape resonances in the (B 1Πu −X 1Σ+g) band system of 39K2 have been recorded by crossed laser-molecular beam techniques. Using optical–optical double resonance, individual rovibrational levels (v″=15–18, J″=3–25) of the K2 state are prepared by Franck–Condon pumping (FCP) in a supersonic nozzle beam. Excitation into quasibound levels below and above the (B 1Πu) state barrier is detected as molecular and atomic (K4 2P3/2→4 2S1/2 only) fluorescence. The resonance transition frequencies and shapes are measured and the results are used (a) to determine the scattering resonance energies, widths, and lifetimes; (b) to compare them with values obtained by a ‘‘maximum internal amplitude’’ approach [R. J. LeRoy and R. B. Bernstein, J. Chem. Phys. 54, 5114 (1971)]; and (c) to check the agreement with exact calculations of the B state potential using the ‘‘inverted perturbation approach (IPA).’’ The bound and quasibound part of the B 1Πu state including the locus (R=8.08±0.05 Å) of the barrier maximum (298±8 cm−1 above the adiabatic dissociation limit) is found in excellent agreement with previous results. The shape resonances are not highly sensitive to the long-range interatomic forces, here the repulsive dipole–dipole resonance interaction.