MULTIPHOTON IONIZATION AND PHOTODISSOCIATION OF (NO)MAR(N) CLUSTERS

Picosecond multiphoton ionization of (NO)(m)Ar(n) clusters produced in a supersonic expansion of NO/Ar gas mixtures has been studied using time-of-flight mass spectrometry. Two-photon ionization with 266 nm photons show that dilute gas mixtures (1% NO/Ar) yield clusters limited to m less-than-or-equal-to 7, but with as many as 37 argon atoms. Magic numbers are observed for NO+Ar12, NO+Ar18, (NO)2+Ar17, NO+Ar22, and (NO)2+Ar21 and are understood in terms of solvation of the NO+ and (NO)2+ by argon in icosahedral arrangements. Four-photon ionization with 532 nm light produces dissociation of the clusters to yield only NO+Ar(n) with n up to 54. This distribution exhibits an additional magic number at n = 54, consistent with the completion of a second solvation sphere about the NO+. The known wavelength dependence for photodissociation of (NO)2+ and (NO)3+ and comparison of MPI spectra obtained with 266, 355, and 532 nm light indicate that the dissociation is occurring in the cluster ions.