Enhanced single-photon double ionization near threshold of substituted benzenes by synchrotron radiation

Abstract

We investigate single photon double ionization (spDI) of substituted benzenes (toluene, chlorobenzene and fluorobenzene) in photon energy of 20–40 eV. We observe that a resonance-like enhancement of spDI, which deviates from the prediction of the “knock-out” mechanism, appears at a specific photon energy near the threshold for halogenated benzenes, but not for toluene. The enhanced spDI occurs if the de Broglie wavelength of the two-electron pseudoparticle matches the size of the conjugated p-π orbital of halogenated benzene. Our study shows that the molecular spDI is not a local event and the molecular orbital plays a pivotal role in double ionization.