On the nature of OH-stretching vibrations in hydrogen-bonded chains: pump frequency dependent vibrational lifetime.
Two-dimensional infrared spectroscopy was carried out on stereoselectively synthesized polyalcohols. Depending upon the stereochemical orientation of their hydroxyl groups, the polyols can either feature linear chains of hydrogen bonds that are stable for extended periods of time or they can display ultrafast dynamics of hydrogen-bond breakage and formation. In the former case, the OH-stretching vibrations and their transition dipoles are substantially coupled, hence prior to vibrational relaxation, the initial OH-stretching excitation is rapidly redistributed among the set of hydroxyl-groups constituting the hydrogen-bonded chain. This redistribution is responsible for an ultrafast loss of memory regarding the frequency of initial excitation and as a result, a pump-frequency independent vibrational lifetime is observed. In contrast, in the latter case, the coupling of the OH-groups and their transition dipoles is much weaker. Therefore, the OH-stretching excitation remains localized on the initially excited oscillator for the time scale of vibrational energy relaxation. As a result inhomogeneous relaxation dynamics with a pump-frequency-dependent lifetime are observed.
Lehrstuhl für Molekulare Physikalische Chemie, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany.
Stephan
S
Knop
Thomas La Cour
TL
Jansen
Jörg
J
Lindner
Peter
P
Vöhringer
D000438:Alcohols / Q000138:chemical synthesis / Q000737:chemistry*; D006860:Hydrogen Bonding; D006878:Hydroxides / Q000737:chemistry*; D011789:Quantum Theory; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism; D013379:Substrate Specificity; D013997:Time Factors; D014732:Vibration
D000438:Alcohols; D006878:Hydroxides; C031356:hydroxide ion