The ultrafast dynamics of excited states in cerium oxide are investigated to access the early moments of polaron formation, which can influence the photocatalytic functionality of the material. UV transient absorbance spectra of photoexcited CeO₂ exhibit a bleaching of the band edge absorbance induced by the pump and a photoinduced absorbance feature assigned to Ce 4f → Ce 5d transitions. A blue shift of the spectral response of the photoinduced absorbance signal in the first picosecond after the pump excitation is attributed to the dynamical formation of small polarons with a characteristic time of 330 fs. A further important result of our work is that the combined use of steady-state and ultrafast transient absorption allows us to propose a revised value for the optical gap for ceria (E_og = 4 eV), significantly larger than usually reported.

One color, mass selected resonant two-photon ionization (1cR2PI) spectra of supersonically expanded bare (R)-(−)indan-1-ol (I_R ) and its complexes with chiral and achiral molecules (solv) have been investigated. The excitation spectrum of bare I_R has been analyzed and discussed on the basis of theoretical predictions at the B3LYP/6-31G** level of theory. The excitation spectra of its diastereomeric complexes with (R)-(−)-and (S)-(+)hexan-2-ol (X_R or X_S , respectively) and water (W) are characterized by significant shifts of their S₀ ← S₁ band origin relative to that of bare I_R . The extent and the direction of these shifts are found to depend upon the structure and the configuration of solv and are attributed to different short-range interactions in the ground and excited [I_R·solv] complexes. In particular the [I_R·W]_n complexes display band origins blue-shifted relative to that of bare I_R , attributed to the presence of an O–H⋯π electrostatic interaction between I_R and W in [I_R·W]_n. The [I_R·X_R] and [I_R·X_S] equilibrium structures have been calculated by a molecular dynamical (MM3) sampling and PM3 semiempirical local optimization.