Negative cluster ions of sodium oxide, NanO−m (m = 1 and 2), were generated by laser vaporization of a sodium rod, and their mass distribution was measured. In the mass spectra, a number of intense peaks compared to neighbors were observed; in NanO−1, the “magic numbers” were observed at n = 9, 21, 27, 35, 41, and 59, and in NanO−2, they were observed at n = 11, 17, 23, 29, 37, 43, and 61. Compared with the magic numbers predicted by the jellium shell model, two and four sodium atoms are increased for the magic numbers by adding one and two oxygen atom(s), respectively. Therefore, it is concluded that (1) no valence electrons of oxygen atoms contribute to form the electronic shells of clusters, and that (2) two sodium atoms in the NanO−m clusters are bound by one oxygen atom, forming an Na2O unit as a spectator.
ASJC Scopus subject areas