Picture of bonding in protonated phosphorus and arsenic clusters. Detection of 3-center bonds from the generalized population analysis

In this report we provide a theoretical support for the existence of noncla ssical 3-center bonding recently invoked to explain the structure of proton ated phosphorus and arsenic X4H+ clusters. For this purpose the electron st ructure of these clusters was analysed using the formalism of the generaliz ed population analysis, in terms of which the eventual presence of multicen ter bonds in a molecule can be directly detected and localized. Our results confirm the presence of 3-center bonding involving X-H-X fragments in thes e clusters.