Magic numbers in (NO)+mArn heteroclusters produced by two-photon ionization in a supersonic expansion

Abstract
Mixed clusters of the form (NO)mArn(m ≤ 4,n ≤ 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+Arn(n= 12,18,22) and (NO)2+Arn(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+Arn heteroclusters and assigned to icosahedral structures. Other cluster ions of the form (NO)+mNO2, (NO)+mN2O, N2O+Arn, and (NO)+mH2O are observed and briefly discussed.