Bulk electronic structure of ${\mathrm{Na}}_{0.35}{\mathrm{CoO}}_2\cdot 1.3{\mathrm{H}}_2\mathrm{O}$

High-energy $(h\nu =5.95\mathrm{}\mathrm{keV})$ synchrotron photoemission spectroscopy (PES) is used to study bulk electronic structure of ${\mathrm{Na}}_{0.35}{\mathrm{CoO}}_2\cdot 1.3{\mathrm{H}}_2\mathrm{O},$ the layered superconductor. In contrast to three-dimensional doped Co oxides, Co $2p$ core level spectra show well-separated ${\mathrm{Co}}^{3+}$ and ${\mathrm{Co}}^{4+}$ ions. Cluster calculations suggest low-spin ${\mathrm{Co}}^{3+}$ and ${\mathrm{Co}}^{4+}$ character, and a moderate on-site Coulomb correlation energy $U_{\mathrm{dd}}\sim 3–5.5\mathrm{eV}.$ Photon dependent valence band PES identifies Co $3d$ and O $2p$ derived states, in near agreement with band-structure calculations.