Comprehensive thermochemistry for the hydration of copper ions

Cross sections for the threshold collision-induced dissociation (TCID) of Cu$^{2+}$(H$_{2}$O)$_{n}$, where n $=$ 8 -- 10, and of CuOH$^{+}$(H$_{2}$O)$_{n}$, where n $=$ 1 -- 4, are measured using a guided ion beam tandem mass spectrometer. In both cases, the primary dissociation pathway is found to be loss of a single water molecule followed by the sequential loss of additional water molecules. In the Cu$^{2+}$ complexes, charge separation to form CuOH$^{+}$(H$_{2}$O)$_{3}$ and H$^{+}$(H$_{2}$O)$_{3}$ is also observed and CuOH$^{+}$(H$_{2}$O) competitively loses both H$_{2}$O and OH. The data are analyzed using a statistical model after accounting for internal and kinetic energy distributions, multiple collisions, and kinetic shifts to obtain 0 K bond dissociation energies (BDEs). In addition, BDEs for the loss of OH from CuOH$^{+}$(H$_{2}$O)$_{n}$ where n $=$ 0 -- 4 are derived using the experimental BDEs for dissociation of CuOH$^{+}$(H$_{2}$O)$_{n}$ and literature values for Cu$^{+}$(H$_{2}$O)$_{n}$. Experimental BDEs are compared to theoretical BDEs determined at several levels of theory with reasonable agreement. Structural information regarding complexes of CuOH$^{+}$(H$_{2}$O)$_{n}$, where n $=$ 2 -- 9, are also obtained using infrared photodissociation spectroscopy (IRPD) in the OH stretching region and comparison to theoretical spectra. The IRPD spectra of all complexes where n $\ge $ 3 are consistent with structures generally having a coordination number (CN) of 4 although CuOH$^{+}$(H$_{2}$O)$_{7}$ exhibits bands characteristic of both CN $=$ 4 and CN $=$ 5 isomers.