Mass analyzed threshold ionization of van der Waals complexes: Binding energies of dibenzofuran·Ar and dibenzo- p-dioxin·Ar

Abstract

The dissociation behavior of the weakly bound van der Waals complexes dibenzofuran·Ar (DBF·Ar) and dibenzo- p-dioxin·Ar (DD·Ar) is investigated by mass analyzed threshold ionization (MATI) spectroscopy. Adiabatic ionization energies (AIEs) were measured for the bare molecules and the complexes, yielding 65 422 cm −1 (DBF), 65 307 cm −1 (DBF·Ar), 61 283 cm −1 (DD) and 61 071 cm −1 (DD·Ar). The breakdown of threshold ion signal at the complex mass and its appearance on the fragment mass channel leads to the following dissociation thresholds E 0 in the ionic ground state: E 0 ⩽ 636 cm −1 for (DBF·Ar) + and E 0 = 739 ± 10 cm −1 for (DD·Ar) +. From the red-shifts of the AIEs of − 115 cm −1 (DBF·Ar) and − 212 cm −1 (DD·Ar) the dissociation energies D 0 in the neutral ground state complexes are found to be D 0 ⩽ 521 cm −1 for DBF·Ar and D 0 = 527 ± 18 cm −1 for DD·Ar. While the ionic dissociation energies differ for both van der Waals systems, their neutral dissociation energies are nearly the same. This points to large charge-induced contributions to the binding energy in DD·Ar because of charge localization at the central, oxygen containing ring.