Fourier transform infrared reorientation

Subtractively normalized interfacial Fourier transform infrared spectroscopy has been used to follow the reorientations of isoquinoline molecules adsorbed at a mercury electrode. Field induced infrared absorption is a major contribution to the intensities of the vibrational band structure of aromatic organic molecules adsorbed on mercury. Adsorbed isoquinoline was observed to go through an abrupt reorientation at potentials more negative than about -0.73 V vs SCE (the actual transition potential being dependent on the bulk solution concentration) to the vertical 6,7 position. 

Electron spectroscopy for chemical analysis (ESCA) [9] and Fourier transform infrared (FTIR) spectroscopy [10] with attenuated total reflectance (ATR) can also be used for routine surface studies. FTIR spectroscopy is known to have the sensitivity to determine the average orientation and reorientation of interfacial chains. But it does not directly provide information on the motion itself. The mobility of a solute in the neighborhood of an alkyl chain can be measured by fluorescence spectroscopy [11]. 

The above equations provide two alternative routes for calculating kinetic coefficients from simulations of a system at equilibrium. Averages in the above equations are ensemble averages, hence the results are ensemble-sensitive. The time correlation functions contain more information than just the kinetic coefficients. The Fourier transforms of time correlation functions can be related to experimental spectra. Nuclear magnetic resonance (NMR) measures the time correlation functions of magnetization, which is related to the reorientation of particular bonds in the polymer molecule inelastic neutron scattering experiments measure the time correlation functions of the atom positions infrared and Raman scattering spectroscopies measure the time correlation function of dipole moments and polarizabilities of the molecules. 

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