Photoelectron spectroscopy of (CO2)n- clusters with 2≤n≤13: Cluster size dependence of the core molecular ion

Abstract

Photoelectron spectra of the negatively charged clusters of CO2 are recorded with 3.49 eV photon energy and appear as bell-shaped, unresolved vibrational envelopes similar to that observed for the monomer ion. The maxima of the photoelectron spectra, found by fitting the envelopes to Gaussian profiles, correspond to the vertical electron detachment energies (VDE) of the clusters. These VDE values, when combined with the previously measured value for CO2-, display sharp discontinuities at cluster sizes n = 2 and n = 6. The magnitudes of these shifts are on the order of 1 eV and are in near quantitative agreement with the calculated difference in VDE between the monomer anion and the D2d form of the dimer anion. We infer from this agreement that the dimer ion is the core of clusters 2≤n≤5 while the monomer ion forms the core for n≥7. The hexamer is special in that both forms are evident in the photoelectron spectra. These structural changes are not manifested as "magic numbers" in the parent spectra, which have been previously observed at n = 4, 7, 10, and 14. © 1988 American Institute of Physics.