Imaging a chemical bond in the molecule frame using microchannel plate based Position Sensitive Detectors and coincidence techniques

Vector correlation is a powerful method for the investigation of photofragmentation of molecules or clusters. It consists of measuring in coincidence the velocity vectors of the electrons and atomic fragments emitted from the same physical event, and provides detailed information about the spectroscopy and intramolecular dynamics of excited states. A new velocity spectrometer which combines imaging and time-resolved detection techniques has been developed and applied to the investigation of dissociative photoionization of diatomic molecules (NO, CO, O-2, H-2, etc.) induced by synchrotron radiation linearly polarized light (P) AB + hv(P) --> A(+) + B* + e in the VUV photon energy range (20 eV less than or equal to hv less than or equal to 40 eV). The (VA+, V-e) velocity vector correlation leads first to the correlation of the fragment ion and electron kinetic energies, which enables to identify and select each fragmentation process and to measure their branching ratios, The angular correlation of the ion and electron velocities for a selected process leads then to the angular distribution of the photoelectrons in the molecular frame, for each orientation of the molecular axis with respect to the linear polarization of the incident light. We illustrate the method by the recent data obtained for dissociative photoionization of NO and O-2. (C) 2002 Elsevier Science B.V. All rights reserved.