The angular distributions of fragment ions from labelledand unlabelled N2O in intense laser fields

Abstract

The mass spectra and angular distributions of fragment ionsarising from a Coulomb explosion of highly charged parent nitrousoxide ions, obtained in the femtosecond regime (~1016 W cm-2), are investigated. The N ion angulardistributions from 14N2O show maxima when the laserpolarization is parallel and orthogonal to the time-of-flightaxis. Measurements with labelled molecules(15N-14N = 16O) indicate that the maxima arisefrom the peripheral and central N atoms in the molecularstructure. The anisotropic distributions may be explained byassuming increased ionization and fragmentation when themolecular axis is parallel to the laser field. The bond angleprior to explosion is determined to be ~140°,irrespective of the charge state of the precursor, andcalculations of the kinetic energies imparted to the fragment ionssuggest that dissociation occurs at the equilibriuminternuclear distance of the neutral molecule.