Anisotropic Ultrafast Dissociation Probed by the Doppler Effect in Resonant Photoemission from [Formula presented]

The resonant Auger spectrum from the decay of F [Formula presented]-excited [Formula presented] is measured. Several lines exhibit a nondispersive kinetic energy as the exciting photon energy is tuned through the resonance region. The F [Formula presented] atomiclike Auger line is split into two components due to the emission of Auger electrons by a fragment in motion, when electron emission is observed along the polarization vector of the light. This Doppler splitting is direct evidence that the core excitation leads to [Formula presented] symmetry lowering, by elongation of a specific [Formula presented] bond preferentially aligned along the polarization vector of the incident photon.