title: Vibrational Spectrum of an Excited State and Huang-Rhys Factors by Coherent Wave Packets in Time-Resolved Fluorescence Spectroscopy.
abstract: Coherent nuclear wave packet motions in an electronic excited state of a molecule are measured directly by time-resolved spontaneous fluorescence spectroscopy with an unprecedented time resolution by using two-photon absorption excitation and fluorescence upconversion by noncollinear sum frequency generation. With an estimated time resolution of approximately 25 fs, wave packet motions of vibrational modes up to 1600 cm-1are recorded for coumarin 153 in ethanol. Two-color transient absorption at 13 fs time resolution are measured to confirm the result. Vibrational displacements between the ground and excited states and Huang-Rhys factors (HRFs) are calculated by quantum mechanical methods and are compared with the experimental results. HRFs calculated by density functional theory (DFT) and time-dependent DFT reproduce the experiment adequately. This fluorescence-based method provides a unique and direct way to obtain the vibrational spectrum of a molecule in an electronic excited state and the HRFs, as well as the dynamics of excited states, and it might provide information on the structure of an excited state through the HRFs.
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, 37673, South Korea.
authors.forename: Gyeongjin
authors.initials: G
authors.lastname: Lee
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, 37673, South Korea.
authors.forename: Junwoo
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, 37673, South Korea.
authors.forename: So Young
authors.initials: SY
authors.lastname: Kim
authors.affiliation: Physics Department, Center for Attosecond Science and Technology, and Max Planck Center for Attosecond Science, Pohang University of Science and Technology (POSTECH), Pohang, 37673, South Korea.
authors.forename: Dong Eon
authors.initials: DE
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, 37673, South Korea.
authors.forename: Taiha
authors.initials: T
authors.lastname: Joo
keywords: Franck-Condon factors; Huang-Rhys factors; coumarin; nuclear wave packets; time-resolved fluorescence