Orientation and vibrational relaxation of acetonitrile at a liquid:solid interface, observed by sum-frequency spectroscopy

• Published in: Chemical physics letters Vol. 356; no. 3; pp. 284 - 290
• Main Authors: Saß, M., Lettenberger, M., Laubereau, A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 22.04.2002; Elsevier Science
• Subjects: Atomic and molecular physics; Exact sciences and technology; Infrared spectra; Molecular properties and interactions with photons; Molecular spectra; Physics; Pump probe spectrometry; Liquid solid interface; Acetonitrile; Vibrational modes; Vibrational relaxation; Time evolution; Sum frequency; Infrared spectra; Experimental study; Organic compounds
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/S0009-2614(02)00331-7

The vibrational spectrum of acetonitrile at the liquid:solid interface with yttrium aluminium garnet is investigated in the CN- and CH-stretching region, using two-color pump–probe sum-frequency spectroscopy in internal total reflexion geometry. An average tilt angle of the molecular symmetry axis with the surface normal of ≅53° is determined suggesting weak interaction with the surface. Measuring the coherent excitation of the symmetric CH 3-transition yields a dephasing time of T 2=420±100 fs. An effective population lifetime of 5.9±1.8 ps and a faster energy redistribution with a time constant of 1.8±1.0 ps are found in the CH-stretching region. Ground state recovery of the molecules at the interface occurs slowly with 150±50 ps, quite different to the bulk liquid.