Hydrogen bonding induced enhancement of Fermi resonances: ultrafast vibrational energy flow dynamics in aniline-d₅.
With hydrogen bonding of the amino group of aniline-d5 we can identify the roles of Fermi enhanced combination and overtone states in intramolecular vibrational re-distribution (IVR) pathways for N-H stretching excitations. Using linear Fourier transform infrared (FT-IR) spectroscopy, ultrafast one- and two-color IR-pump-IR-probe spectroscopy, and femtosecond two-dimensional IR spectroscopy, we can identify the primary accepting modes for N-H stretching excitations. In particular, a key role is played by the δ(NH2) bending degree of freedom, either via its δ = 2 overtone state or via a combination state with the ν(C═C) ring stretching mode. No significant transient population in these Fermi enhanced combination/overtone states can be observed, a consequence of similar decay rates of these Fermi enhanced combination/overtone states and of the N-H stretching states. A similar magnitude of the transient response of the two fingerprint modes regardless of direct excitation of the Fermi enhanced combination/overtone levels or of the N-H stretching states suggests an underlying coupling mechanism facilitating common IVR pathways. This mechanism is expected to be of general importance for other organic compounds with hydrogen-bonded amino groups, including DNA bases.
Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie , , Max Born Strasse 2A, D-12489 Berlin, Germany.
Rene
R
Costard
Christian
C
Greve
Henk
H
Fidder
Erik T J
ET
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