Complexation dynamics of CH3SCN and Li+ in acetonitrile studied by two-dimensional infrared spectroscopy

Youngah Kwon, Sungnam Park

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9 Citations (Scopus)


Ion-molecule complexation dynamics were studied with CH3SCN and Li+ in acetonitrile by vibrationally probing the nitrile stretching vibration of CH3SCN. The nitrile stretching vibration of CH3SCN has a long lifetime (T1 = ∼90 ps) and its frequency is significantly blue-shifted when CH3SCN is bound with Li+ ions to form a CH3SCN⋯Li+ complex in acetonitrile. Such spectral properties enable us to distinguish free CH3SCN and the CH3SCN⋯Li+ complex in solutions and measure their dynamics occurring on hundred picosecond timescales. For the complexation between CH3SCN and Li+ in acetonitrile, the change in enthalpy (ΔH = -7.17 kJ mol-1) and the change in entropy (ΔS = -34.4 J K-1 mol-1) were determined by temperature-dependent FTIR experiments. Polarization-controlled infrared pump-probe (IR PP) spectroscopy was used to measure the population decay and orientational dynamics of free CH3SCN and the CH3SCN⋯Li+ complex. Especially, the orientational relaxation of the CH3SCN⋯Li+ complex was found to be almost 3 times slower than those of free CH3SCN because Li+ ions strongly interact with the neighboring solvents. Most importantly, the complexation dynamics of CH3SCN and Li+ in acetonitrile were successfully measured in real time by 2DIR spectroscopy for the first time and the dissociation and association time constants were directly determined by using the two-species exchange kinetic model. Our experimental results provide a comprehensive overview of the ion-molecule complexation dynamics in solutions occurring under thermal equilibrium conditions.

Original languageEnglish
Pages (from-to)24193-24200
Number of pages8
JournalPhysical Chemistry Chemical Physics
Issue number37
Publication statusPublished - 2015 Aug 13

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ASJC Scopus subject areas

  • General Physics and Astronomy
  • Physical and Theoretical Chemistry


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