Electronic spectroscopy and photodissociation dynamics of Co2+–methanol clusters: Co2+(CH3OH)n (n = 4–7)

Abstract

Solvated cluster ions Co²⁺(CH₃OH)_n (n = 4–7) have been produced by electrospray and studied using photofragment spectroscopy. There are notable differences between the photodissociation spectra of these complexes and the analogous water complexes. Co²⁺(CH₃OH)₆ absorbs significantly more strongly than Co²⁺(H₂O)₆. The photodissociation spectra of Co²⁺(CH₃OH)_n (n = 4, 5 and 6) are very similar, which suggests that they share the Co²⁺(CH₃OH)₄ chromophore, with additional solvent molecules in the second shell. In contrast, our earlier studies indicate that Co²⁺(H₂O)₆ is six coordinate, and its spectrum is significantly different from that of Co²⁺(H₂O)₄. The larger clusters Co²⁺(CH₃OH)_n (n = 5–7) dissociate by simple loss of one or more solvent molecules. Larger clusters tend to lose more solvent molecules, especially at higher photon energies. As with the corresponding water cluster, Co²⁺(CH₃OH)₄ photodissociates by proton transfer through a salt-bridge intermediate. This is accompanied by a modest kinetic energy release of 170 kJ mol⁻¹ and occurs with a lifetime of 145 ns.