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

The mass spectra and angular distributions of fragment ions arising from a Coulomb explosion of highly charged parent nitrous oxide ions, obtained in the femtosecond regime (similar to 10(16) W cm(-2)), are investigated. The N ion angular distributions from (N2O)-N-14 show maxima when the laser polarization is parallel and orthogonal to the time-of-flight axis. Measurements with labelled molecules (N-15-N-14=O-16) indicate that the maxima arise from the peripheral and central N atoms in the molecular structure. The anisotropic distributions may be explained by assuming increased ionization and fragmentation when the molecular axis is parallel to the laser field. The bond angle prior to explosion is determined to be similar to 140 degrees, irrespective of the charge state of the precursor, and calculations of the kinetic energies imparted to the fragment ions suggest that dissociation occurs at the equilibrium internuclear distance of the neutral molecule.