Photoelectron spectroscopy of (CO 2) nH 2O − (2⩽ n⩽8) clusters

Abstract

Photoelectron spectra of negatively charged clusters composed of carbon dioxide and water molecules, (CO 2) n H 2O − (2⩽ n8), were measured at the photon energy of 3.49 eV. The spectra show unresolved broad features, which are approximated by Gaussians. The vertical detachment energies (VDEs) were determined from the maxima of the spectra. The VDE- n plots exhibit a sharp discontinuity between n=3 and 4; the VDE value is ≈3.5 eV at n=3, while it drops down abruptly to 2.59 eV at n=4. This discontinuity in VDE is ascribed to “core switching” at n=4; a C 2O − 4 dimer anion is the core of (CO 2) n H 2O − for n⩽3, while a monomer CO − 2 becomes the core for n⩾4.