Chemical reaction of silicon clusters with nitric oxide by using FT-ICR mass spectrometer

Chemical reaction of small silicon cluster ions (Si_n⁺:13, 15 ≤i ni ≤i 29) with nitric oxide was studied by using the FT-ICR (Fourier Transform Ion Cyclotron Resonance) mass spectrometer. Silicon clusters were generated by a pulsed laser-vaporization supersonic-expansion cluster beam source directly connected to the FT-ICR mass spectrometer. Fully thermalized and mass-selected clusters were reacted with NO in the ICR cell. The primary reaction was the exchange of a silicon atom with a nitrogen atom as Si_n⁺ + NO → Si_n-1N⁺ + SiO. Then, smaller clusters than Si₂₃N⁺ (with exceptions for Si₁₆N⁺ and Si₂₀N⁺) fragmented to much smaller clusters. It was explained that in general smaller clusters could not survive with the exothermal reaction heat. On the other hand, the magic number clusters of Si₁₆N⁺ and Si₂₀N⁺ probably represented the geometrical special stability.