title: Interplay between temperature-activated vibrations and nondipolar effects in the valence excitations of the CO₂ molecule.
abstract: We report a study on the temperature dependence of the valence electron excitation spectrum of CO2 performed using nonresonant inelastic X-ray scattering spectroscopy. The excitation spectra were measured at the temperatures of 300 and 850 K with momentum-transfer values of 0.4-4.8 Å(-1), i.e., from the dipole limit to the higher-multipole regime, and were simulated using high-level coupled cluster calculations on the dipole and quadrupole level. The results demonstrate the emergence of dipole-forbidden excitations owing to temperature-induced bending mode activation and finite momentum transfer.
authors.affiliation: Department of Physics, University of Helsinki , P.O. Box 64, FI-00014 Helsinki, Finland.
authors.forename: Juho
authors.initials: J
authors.lastname: Inkinen
authors.forename: Johannes
authors.initials: J
authors.lastname: Niskanen
authors.forename: Arto
authors.initials: A
authors.lastname: Sakko
authors.forename: Kari O
authors.initials: KO
authors.lastname: Ruotsalainen
authors.forename: Tuomas
authors.initials: T
authors.lastname: Pylkkänen
authors.forename: Szabolcs
authors.initials: S
authors.lastname: Galambosi
authors.forename: Mikko
authors.initials: M
authors.lastname: Hakala
authors.forename: Giulio
authors.initials: G
authors.lastname: Monaco
authors.forename: Keijo
authors.initials: K
authors.lastname: Hämäläinen
authors.forename: Simo
authors.initials: S
authors.lastname: Huotari