Phosphorus clusters: Synthesis in the gas-phase and possible cagelike and chain structures

Experimental results on the gas-phase formation of neutral and cationic phosphorus clusters are presented. The clusters were synthesized by visible (532 nm) or UV (193 nm) laser ablation of crystalline red phosphorus under high vacuum conditions and were analyzed using TOF mass spectrometry. Neutral P_n clusters produced by 532-nm ablation are found to be even-numbered while P _n ⁺ cations are mainly odd-numbered, with P ₇ ⁺ and P ₂₁ ⁺ being the most abundant ions. For UV laser ablation, stable compound clusters, neutral P₇H₃ and P₂₃H₅, and cations P₂₃H ₆ ⁺ were synthesized for the first time. The formation of P_n clusters by thermal vaporization of red phosphorus into a cold He gas was also investigated and only small clusters (n<6) were found. Possible structures of the observed phosphorus clusters, as well as their formation mechanisms under different conditions, are discussed.