吉田 弘幸

Photoelectron spectra of (CO2)nH2O- (2 less-than-or-equal-to n less-than-or-equal-to 8) and (CO2)n(H2O)2- (1 less-than-or-equal-to n less-than-or-equal-to 2) 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 as a function of the cluster size. For (CO2)nH2O-, the VDE-n plots exhibit a sharp discontinuity between n = 3 and 4; the VDE value is almost-equal-to 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 C2O4- dimer anion forms the core of (CO2)nH2O- for n less-than-or-equal-to 3, while a monomer CO2- is the core for n greater-than-or-equal-to 4. The (CO2)2(H2O)2- ion has a VDE of 2.33 eV, indicating the presence of a CO2- monomer core in the binary clusters containing two H2O molecules.