Düsseldorf 2007 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 21: Femtosecond Spectroscopy II

MO 21.1: Fachvortrag

Dienstag, 20. März 2007, 10:30–11:00, 6D

Ab initio simulations of linear and nonlinear infrared spectroscopy — •Jens Dreyer — Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Strasse 2A, D-12489 Berlin, Germany

Vibrational excitations play a central role for the ultrafast nonequilibrium dynamics of intra- and intermolecular hydrogen bonds. The stretching vibration of hydrogen-bonded O-H and N-H groups undergoes pronounced changes of frequency and vibrational line shape upon hydrogen bonding and frequently displays subpicosecond population lifetimes, which are much shorter than the corresponding lifetimes of free O-H/N-H groups. Relaxation via fingerprint mode overtone and combination bands mediated by Fermi resonance coupling as well a decay into low-frequency hydrogen bond modes have been invoked to explain such short lifetimes.

It will be shown how density functional theory calculations of anharmonic couplings in hydrogen bonds are used to address the linear and nonlinear vibrational spectroscopy of hydrogen bonds [1]. We predict and analyze multidimensional signatures of hydrogen bond coupling mechanisms by ab initio simulations of 2D IR spectra. The particular case of acetic acid dimers will be presented [2]. We address the lifetime shortening of 7-azaindole N-H stretching excitations in going from the monomer to the dimer as well as the mechanisms underlying the complex substructure of the N-H stretching infrared absorption band.

[1] J. Dreyer J. Chem. Phys. 2005, 122, 184306 ; [2] J. Dreyer Int. J. Quantum Chem. 2005, 104, 782.