Electronic shell structure in monoxides and dioxides of sodium

Metal-metal bonding interactions are important for the structure and proper ties of sodium-rich monoxide and dioxide clusters NanO, NanO2 n less than o r equal to 10. DFT calculations show that such bonding is due to occupied m olecular orbitals of mostly Na:3s character and provide evidence that these orbitals resemble the 1s, 1p electronic shells of pure metal clusters. Cal culated properties of the sodium oxides (ionisation potential and sodium ab straction energy) follow those of pure sodium clusters in both magnitude an d overall trend. Structural anomalies can also be explained by the electron ic shell model, as illustrated with clusters possessing four 'metallic' ele ctrons (1s(2)1p(2)). Singlets show Jahn-Teller distortion to prolate shapes ; triplets distort to become oblate. In addition, the shell model rationali ses the stereoelectronic conditions for the metal-to-peroxide electron tran sfer which leads to O-O cleavage.