Photoemission in the molecular frame using the vector correlation approach: from valence to inner-valence shell ionization

The (VA+, V-e, e) vector correlation method, combining imaging and time-of-flight resolved electron-ion coincidence techniques, is used to probe dissociative photoionization (DPI) of simple molecules induced by VUV polarized synchrotron radiation, to obtain the 1(0,, 0,) molecular frame photoelectron angular distributions (MFPADs). We focus on examples where DPI is induced by valence shell and inner-valence shell excitation. For valence shell ionisation, we report the results of a complete experiment for DPI of O-2 via the O-2(+)(3(2) Pi(u)) ionic state, performed with a single circular polarization of the light at a photon excitation energy hv = 24.4 eV. A significant circular dichroism effect characterizes electron emission in the molecular frame. Inner-valence shell ionization induced by linearly polarized light is reported for the CO2 and N2O isoelectronic molecules selecting two specific satellite lines using light with hv similar or equal to 35 eV. For both valence and inner-valence ionization, the measured MFPADs are compared with multichannel configuration interaction calculations, as well as with the prediction of a simple theoretical model of photoionization dynamics that probe the role of the initial state molecular orbital and which is presented in this special issue. (C) 2004 Elsevier B.V. All rights reserved.