Interatomic resonant Auger effects in core-level photoemission from NO and CS2 molecules

Core-level interatomic resonant Auger in isolated molecules can take place when the photon energy is tuned to a resonant core-level excitation of an atom neighbouring the electron-emitter atom, provided that the emitter atom has smaller ionization energy of core electrons than the resonant energy. A multi-atomic nature of the Auger is a molecular analogue of multi-atom resonant photoemission (MARPE) observed in a condensed phase. This phenomenon in linear molecules, NO and CS2, has been explored by means of a photoelectron-fragment-ion-fragment-ion multi-coincidence velocity mapping technique. The N 1s (S 2p) photoionization experiments have been conducted at the O 1s -> pi* (C 1s -> pi*) resonance energy and at the off-resonance one, in which photoelectron angular distributions were obtained with respect to the recoil axis of the fragment ions produced by an Auger decay following the core-level photoemission. A resonance enhancement was observed along the photon polarization direction and this effect strongly depends on the relative geometry of the polarization vector and the recoil axis. By comparing the N 1s photoemission of NO with the S 2p photoemission of CS2, it is shown that the resonance enhancement also depends on the core-orbital characters that participate in the process. Such phenomenon should be considered to be general and the present results of the simplest system thus shed new light on photoemission studies for both isolated molecules and condensed systems consisting of different elements.