Interaction of third-row main group dicarbides, C2X (X = K–Br) with molecular oxygen: A density functional study

In this work, we present our calculations, based on density functional theory (DFT) to investigate the molecular adsorption of O2 on the third-row main group dicarbides, C2X, with X = K, Ca, Ga, Ge, As, Se, Br. The structures of the host C2X clusters, except C2Ga and C2Ge, are found to be weakly modified in presence of O2 adsorbate. C2Ga and C2Ge clusters which show cyclic ground-state structures become linear while interacting with O2 molecule. It is observed that the O–O stretching frequencies in C2XO2 are red-shifted in comparison to that in O2 molecule, whereas the C–C stretching frequencies are found to be increased. The calculated adsorption ( E ads ) and Gibbs’ free energies (dG) for the clusters with even number of electrons are found to follow the order of C2CaO2 > C2GeO2 > C2SeO2, whereas the increase in O–O bond lengths follows the reverse order, i.e. (O–O)C2SeO2 > (O–O)C2GeO2 > (O–O)C2CaO2. On the other hand, for the clusters with odd number of electrons, E ads and O–O bond lengths follows almost the same order. Existence of disynaptic basins V (C, O) and their corresponding lower relative fluctuation and higher covariance values based on ELF topological analysis infers that the electrons are delocalized in these areas giving rise to shared-electron interactions. In addition, large electron density at the bond critical point (BCP) between C (of host cluster) and O (of adsorbate) also infers the C–O bonding to be shared-type. This fact is also found to be supported by large delocalization index for C and O as compared to that for X and O.