Vibrational exciton cluster states, percolation and pairwise interactions: Benzene A2u band

Abstract

Infrared spectra of isotopic mixed benzene crystals (C e 6 H /C D) 6 6 were obtained at about boiling nitrogen temperature, with emphasis on the umbrella mode (at about 700 cm-'). These are interpreted in terms of guest cluster spectra (monomers, pairs, etc.) up to about 55% mole. Static percolation sets in at about 50%. resulting in an extended exciton band. The line positions, line intensities and the percolation concentration all aBee quantitatively with an effective Z-dimensionaf sqtuzre lartice exciton inferactiozz topokz~~. This means that very short range, nearest neighbor interchange equivalent, excitation exchange interactions dominate over the long range transition-dipole type terms even in this most intense, dipole allowed IR band. These results fully support our recent picture of the umbrella mode exciton baitd, in both solid and liquid benzene. Similarities between these solid and liquid exciton bands are pointed out. The existence of pseudolocalized states, in the middle of the energy band of the extended states, is illustrated.

Probing the folding of mini-protein Beta3s by two-dimensional infrared spectroscopy; simulation study

“…Simulation of the 1D and 2DCS IR spectra was carried out according to an approach described by Zhuang and Mukamel [ 28 , 46 - 48 ], as implemented in the SPECTRON [ 28 ], software package. The Local Amide Hamiltonian (LAH) approach was applied to describe the peptide structures in our calculations [ 49 - 53 ]. The Hamiltonian parameters were provided by Mukamel et al as implemented in SPECTRON [ 28 ].…”

Signatures of β-Peptide Unfolding in Two-Dimensional Vibrational Echo Spectroscopy: A Simulation Study

“…An early study of symmetric model peptides demonstrated that the transition dipole coupling between CO stretching modes in different peptide bonds results in a delocalization of the amide-I states. These states can be described by vibrational excitons, , using the Frenkel exciton model developed originally to treat delocalized electronic , and vibrational − excitations in molecular crystals and aggregates. The dependence of the dipole−dipole coupling on the relative orientations and distances of the interacting dipoles yields an amide-I band signature that depends on the three-dimensional structure of the protein.…”