Determination of time scales for charge-transfer screening in physisorbed molecules

Using photoionization, photoabsorption, and deexcitation spectroscopies, the dynamics of the N 1s core-hole states for ${\mathrm{N}}_2$ physisorbed on graphite has been investigated. In the photoemission spectrum only the ionic 1${\mathit{s}}^{\mathrm{-}1}$ state is observed. The Auger spectrum shows decay from both this ionic and a neutral 1${\mathit{s}}^{\mathrm{-}1}$1${\mathrm{\pi }}_{\mathit{g}}$ intermediate state created by charge transfer from the substrate. The neutralization occurs with a characteristic time ${\mathrm{\tau }}_{\mathrm{CT}}$=9×${10}^{\mathrm{-}15}$ s. The coupling with the substrate is weak, preserving the gas-phase triplet-singlet splitting of the neutral intermediate state.