Method of Heavily Doped Isotopic Mixed Crystal for Determination of Exciton Splittings and Normal Modes: Raman Spectra of Naphthalene

Abstract

Recent developments on concentrated mixed crystal exciton spectra enabled us to develop new qualitative and quantitative criteria for the identification of vibrational exciton splittings: Observation of an appropriately structured spectrum in the exciton k7"'O gap. This is especially useful for Raman Spectra where the ideal mixed crystal approach is not very useful due to the low intensity of very dilute solid solutions and where the classical pure crystal polarization criterion is difficult to use, especially at low temperatures. The conflicting literature assignments of Raman exciton splittings for naphthalene are resolved: the eight major splittings (~4 cm-I) found here have been missed before, while all major "Davydov" splittings (2:4 em-I) recently reported are invalidated. The clarification of exciton splittings leads to some clarification of the normal mode assignments in the naphthalene molecule. A helpful criterion is utilized here as well: isotopic substitution has mild and predictable effects on the exciton bandwidth and splitting.

Ultrafast Chemistry of Nanoenergetic Materials Studied by Time-Resolved Infrared Spectroscopy: Aluminum Nanoparticles in Teflon

“…The problem is that the stretching transitions for CF 2 of PTFE (1155 and 1220 cm -1 ) and CFO of dioxole (1150 and 1245 cm -1 ) are nearly coincident, as indicated by the dashed lines in Figure a,b, due to the small mass difference between O and F . Bands of this sort in binary mixed crystals or binary copolymers having vibrational frequencies ν a and ν b and vibrational bandwidths Δν a and Δν b are usually described as being in either the separated band limit or the amalgamation limit. − The separated band limit occurs when the splitting |ν a − ν b | ≫ Δν. In this case, copolymers have two separate transitions whose relative intensities reflect the composition.…”