A theoretical study on structures, energetics, and spectra of Br-.nCO2 clusters: towards bridging the gap between...

Structures, energetics, and spectra of Br(-).nCO(2) (n = 1-8) clusters are studied based on ab initio electronic structure theory. The geometry of each size of clusters is evaluated by employing second-order Moller-Plesset (MP2) perturbation theory. It is observed that the solvent CO(2) molecules approach the bromide moiety from one side in an asymmetric fashion except for the Br(-).8CO(2) cluster. Simple electrostatic model for charge-quadrupole interactions is valid for the Br(-).nCO(2) clusters. Reduced variational space based energy decomposition method shows that the electrostatic interaction is the major component and polarization and charge transfer energies are the other significant components of the total interaction energy. Both adiabatic and vertical electron detachment energies and solvation energies are calculated at MP2 level of theory. We have observed an excellent agreement between theory and experiment for the vertical detachment and solvation energies. Calculated quantities based on the analytical expression which connects the finite domain to macroscopic one are found to be very good in agreement with the available experimental results. The present study reveals a 2.6 eV increase in the detachment energy of bromide anion due to the solvation effect of CO(2), which is relatively small compared to that of the corresponding 4.7 eV increase in detachment energy in water.