MAGIC NUMBERS IN (NO)M+ARN HETEROCLUSTERS PRODUCED BY 2-PHOTON IONIZATION IN A SUPERSONIC EXPANSION

Mixed clusters of the form (NO)(m)Ar(n)(m less-than-or-equal-to 4,n less-than-or-equal-to 22) are produced in a supersonic expansion and photoionized by nonresonant two-photon absorption of 266 nm photons. The ions are subsequently separated and detected by time-of-flight mass spectrometry. Anomalously large relative intensities are observed for the cluster ions, NO+Ar(n)(n = 12,18,22) and (NO)2+Ar(n)(n = 17,21), and are attributed to extra stability of these ions. These "magic numbers" at (m + n) = 13,19,23 are compared to those observed in rare gas clusters and other M+Ar(n) heteroclusters and assigned to icosahedral structures. Other cluster ions of the form (NO)m+NO2, (NO)m+N2O, N2O+Ar(n), and (NO)m+H2O are observed and briefly discussed.