An ab Initio Study on the Structure, Energetics, and Spectra of Cl^-···(CO₂)_n Clusters

Structures, energetics, and photoelectron spectral properties of Cl^-···(CO₂)_n (n = 1-8) clusters are studied by ab initio electronic structure methods, namely, Møller-Plesset second-order perturbation theory (MP2) correlated consistent, aug-cc-pvtz basis functions. The most stable structure for each size is evaluated by using both bottom-up and top-down approaches. It is observed that CO₂ molecules approach to the chloride anion in an asymmetric way except for Cl^-···(CO₂)₈ cluster. We do observe the applicability of the simple classical electrostatic model for charge-quadrupole interactions to the solvation of the chloride anion by the solvent CO₂. Both vertical electron detachment energies and solvation energies are calculated for all the clusters at the MP2 level. We do observe an excellent agreement between theory and experiment for the vertical detachment energy, solvation energy, and gas phase detachment energy of chloride anion. It is also observed that the detachment energy of the chloride anion is increased by 4.09 eV due to the solvation effect of bulk CO₂ and it is quite small in contrast to the increase of 5.29 eV due to the solvation effect of polar solvent, water.