Infrared spectroscopy intramolecular order

Since infrared spectroscopy also provides information about physical structure, infrared imaging can be used to determine spatial distribution of physical properties as well. Some of the properties include intermolecular and intramolecular order, hydrogen bonding, protein secondary structure, complexation and functional group orientation. 

A new approach to simulate multidimensional infrared spectroscopy was suggested by Jeon and Cho [840]. They compute the third-order vibrational response function in the classical hmit using MD simulations in combination with QM/MM. In this investigation it could be shown that QM/MM approaches are needed for reliable predictions. Conventional classical force fields are too inaccurate since they cannot describe the intramolecular vibrational anharmonicities which are essential for the production of the nonlinear signal. QM/MM force fields are found to reproduce 2D spectra for V-methylacetamide and carbon monoxide, each solvated in water, in nice agreement with their experimental counterparts. 

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