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Gas-phase reactions are reliable strategies to explore the stability and activity of metal clusters, which can provide the information of products and the cluster activities by comparing the changes of the X, Y-axis of the mass spectrum before and after the reaction.Combined with ab initio calculation, we can deeply explore the structure of clusters, reaction intermediates and final products, explore the reaction thermodynamics and kinetic process,and reveal the essence and relationship between cluster structure,stability and reaction activity.In this paper,by investigating the gas-phase reaction mass spectra of Cun--clusters with NO and O2,,Agn- clusters with O2,and further combined with the ab initio calculation,novel open shell superatoms Cu18-,double closed shell superatoms Ag17- with unique stability are reported.Besides,we demonstrated the donation and back donation interactions between NO and Cun--.Chemisorption of O2 on Cu-2n+1,Cu-2n+1(or Ag-2n) clusters follows the double and single electron transfer mechanism, respectively.Among them, the behavior of O2 on Cu;;-is enabled by the spin conservation rule.By analogizing the cluster and O2 as base and acid respectively, we found a phenomenon that clusters with different alkalis pass through different degrees of spin excitation or dissociation barriers,and finally release almost the same heat for O2 dissociation. Based on this, a fully new mechanism of O2 on metal clusters was proposed: leveling effect of spin accommodation.Calculations of energy decomposition analysis-natural orbitals for chemical valence show that the activities of Cu; clusters towards NO and O2,Ag; clusters toward O2 are closely related to cluster geometry, electronic shell arrangement and energetics data. [ABSTRACT FROM AUTHOR]