The P-4 center dot center dot center dot Li+ ion in the gas phase: A planetary system

Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT ICR) has re vealed the existence of the P4Li+ ion as a stable species in the gas phase. High-level ab initio calculations show that P4Li+ appears as a "planetary system" wherein the lithium cation can easily move around the P-4 moiety al ong paths (or "orbits") connecting the points above the middle points of th e P-P edges with points above the center of the PPP faces, the movement tow ard the corners of the tetrahedron being the less favored. Due to symmetry, this orbiting is 4-fold degenerate.