Adsorption and reactivity of CO₂ on potassium-covered Re(001)

The interaction of CO₂ with potassium-covered Re(001) has been investigated. This system has been studied by means of work function (Δφ), optical second harmonic generation (SHG), and temperature-programmed desorption (TPD) measurements. Strong electronic interaction between carbon dioxide and potassium is observed upon adsorption at 90 K. This is indicated by a rapid quenching of the SHG signal of K following postadsorption of CO₂, with a quenching cross section of 70 Ų. Work function change measurements are consistent with such interaction, evidenced by an undepolarization effect, namely, further decrease of the work function upon CO₂ adsorption, below the minimum obtained by pure potassium. In the presence of potassium, the dissociation probability of 0.5 ML adsorbed carbon dioxide increases from 0.5 on the clean metal surface to 0.85 on 1 ML potassium-covered Re(001), information obtained from TPD measurements following heating to 1250 K. It is concluded that a K-CO₂ surface compound is formed upon adsorption at 95 K on the potassium-covered surface.