Spectroscopy and Photochemistry of Sodium Chromate Ester Cluster Ions

In the present study, we investigate the spectroscopy and photochemical behavior of chromate ester cluster ions in vacuo in the visible and near-UV. Chromate ester cluster ions Na n [CrO3(OCH3)] n+1 – (n = 1, 2) are generated by electrospray ionization of sodium dichromate in water and methanol. Upon irradiation with photon energies between 2 and 5.6 eV, dissociation occurs. The photodissociation spectra of these ions are very similar to the UV/vis absorption spectra of the sample solution with solvatochromic shifts less than 0.1 eV. The electronic excitations in this photon energy range are assigned to ligand-to-metal charge transfer from the oxygen ligands to the chromium within the chromate ester. Fragment channels corresponding to intracluster reactions involving reduction of the metal centers as well as evaporative processes leading to the loss of a neutral Na[CrO3(OCH3)] salt unit are observed. The results are discussed in the framework of organometallic redox mechanisms and density functional theory.