Experimental study of the dissociation of selected internal energy ions produced in low quantities: Application to N2O+ ions in the Franck-Condon gap and to small ionic water clusters

A new experimental apparatus to study gas phase photoionisation of cold species and clusters is available at SuperAco, the Orsay synchrotron radiation facility. This equipment brings together the advantages of synchrotron radiation, supersonic expansions, and photoelectron-photoion coincidence techniques. We present here two types of preliminary results to illustrate some important technical features. The use of multicoincidences to study the photoionisation of N2O in the Franck-Condon gap between the X ground state and the A first excited state clearly reveals that the parent ion should be fully predissociated above 15.1 eV. A specific design of a Wiley-McLaren type time-of-flight (TOF) spectrometer for ion detection and analysis allows us to distinguish between the ionic clusters, resulting from direct ionisation of neutrals and those resulting from dissociation of larger ionic clusters, as will be shown for small water clusters, especially for the dimer.