Photoionization and photofragmentation of B_xN_y clusters produced by photoablation of boron nitride followed by supersonic expansion cooling

Abstract

Photoablation of isotopically pure boron metal and hexagonal boron nitride with a 532 nm laser, followed by supersonic expansion cooling, produces a variety of Bx and BxNy clusters, which are detected by photoionization of the neutral clusters with a 194 nm laser, followed by time-of-flight (TOF) mass spectrometry. Under certain experimental conditions, the mass spectrum derived from boron nitride shows resolved peaks corresponding to the clusters By+1Ny+. Under different experimental conditions, the mass spectrum shows an unresolved region corresponding to clusters ranging from atomic mass unit 100-1000 as well as resolved peaks, corresponding to Bx+ clusters for x = 2-100. These resolved peaks grow with increasing photoionization fluence, while the envelope of the unresolved region changes shape and grows with a diminished dependence on fluence. These data are interpreted as evidence that the unresolved clusters are being photofragmented as well as photoionizated by the 194 nm radiation, and the products of such photofragmentation are the aforementioned Bx+ clusters.