Long-range interactions from the self-broadened profile of Zn (41P1–41S0) and Cd (51P1–51S0) lines: correction of the interaction potential parameters

Abstract

The self-broadened absorption profile of Zn (213.8 nm) and Cd (228.8 nm) lines are measured and carefully analysed. The interaction potentials for the electronic states 0+u and 1u dissociating into (41P1 + 41S0) and (51P1 + 51S0) for Zn2 and Cd2, respectively, are derived in the long-range region of (11–25) Å. It is found that although the resonance dipole–dipole interactions, Cm3/R3, dominate in this region, the higher order van der Waals terms, Cm6/R6 are also not negligible. The coefficients Cm3 and the differences ΔCm6 between Cm6 for each of the 0+u and 1u excited states and Cg6 for the ground state of both molecules are determined. For the energy in eV and R in Å it is found that C03 = −23.74 ± 0.40, ΔC06 = −483 ± 30 and C13 = 11.87 ± 0.20, ΔC16 = −227 ± 20 for Zn2, as well as C03 = −24.54 ± 0.10, ΔC06 = −280 ± 15 and C13 = 12.27 ± 0.05, ΔC16 = −215 ± 10 for Cd2. A problem of the Cg6 coefficient for the considered systems is discussed accepting finally the following values: −178±10 and −291±15 eVÅ6 for Zn2 and Cd2, respectively. Thus, for the excited states involved, one obtains C06 = −661 ± 40 and C16 = −405 ± 30 for Zn2 as well as C06 = −571 ± 30 and C16 = −506 ± 25 for Cd2. The C6m coefficients have never been determined experimentally in any of these cases and only for Zn2 were they calculated by Ellingsen et al (2001 J. Phys. B: At. Mol. Opt. Phys. 34 2313) by means of a time-dependent gauge-invariant method—a variation-perturbation approach. Our experimental results for this case agree very well with theoretical predictions.