title: Two-photon absorption cross sections: an investigation of solvent effects. Theoretical studies on formaldehyde and water.
abstract: The effects of a solvent on the two-photon absorption of microsolvated formaldehyde and liquid water have been studied using hybrid coupled-cluster/molecular mechanics (CC/MM) response theory. Both water and formaldehyde were considered solvated in water, where the solvent water molecules were described within the framework of molecular mechanics. Prior to the CC/MM calculations, molecular dynamics simulations were performed on the water/formaldehyde and water/water aggregates and many configurations were generated. By carrying out CC/MM response calculations on the individual configurations, it was possible to obtain statistically averaged results for both the excitation energies and two-photon absorption cross sections. For liquid water, the comparison between one- and two-photon absorption spectra is in good agreement with the experimental data available in the literature. In particular, the lowest energy transition occurring in the one-photon absorption spectrum of water only occurs with a relatively small strength in the two-photon absorption spectrum. This result is important for the interpretation of two-photon absorption data as these results show that in the absence of selection rules that determine which transitions are forbidden, the spectral profile of the two-photon absorption spectrum can be significantly different from the spectral profile of the one-photon absorption spectrum.
authors.affiliation: Department of Chemistry, University of Arhus, Langelandsgade 140, DK-8000 Arhus C, Denmark. m.j.paterson@hw.ac.uk
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Paterson
authors.forename: Jacob
authors.initials: J
authors.lastname: Kongsted
authors.forename: Ove
authors.initials: O
authors.lastname: Christiansen
authors.forename: Kurt V
authors.initials: KV
authors.lastname: Mikkelsen
authors.forename: Christian B
authors.initials: CB
authors.lastname: Nielsen