Fundamental Molecular Vibrations Research Articles

Near-Infrared Spectroscopy of Organic Substances

Abstract The near-infrared spectral region is generally defined as the wavelength range from 700 nm to about 2500 nm, although there is considerable variation in wavelength ranges of the different instrument types. The absorption bands in this region are due to overtones and combinations of the fundamental mid-IR molecular vibration bands. The energy transitions are between the ground state and the second or third excited vibrational states. Because higher energy transitions are successively less likely to occur, each overtone is successively weaker in intensity. Since the energy required to reach a second o r third level excited.

The vibrational spectrum of crystalline cyclobutanone

Infrared and Raman phonon spectra of crystalline cyclobutanone have been studied. The i.r. measurements have been carried out by means of polarized radiation at different temperatures below the freezing point. The spectra show that only one crystalline phase is stable in the range of temperatures 241-100°K. A new assignment of some fundamental molecular vibrations has been carried out using group-frequency concepts, Raman polarization data and dichroic behavior of peaks in the oriented solid samples. Correlation field splitting of the molecular motions seems to indicate that cyclobutanone crystallizes in the monoclinic system, lying the molecules at general positions of the unit-cell.

Motions of Molecules in Condensed Systems. IX. Infrared Absorption Anisotropy and Induced Molecular Motion in a Single Crystal of Benzene

Infrared absorption spectra were observed with radiation polarized linearly along each of the two extinction axes contained in a thin cross section from a single crystal of benzene grown especially for this purpose. The spectra indicate consistently that the cross section was the 010 plane, that they record separately the absorptions polarized along the a-axis and the c-axis, respectively. The anisotropies of the induced absorptions exhibited by five fundamental molecular vibrations (ones that appear only in spectra for condensed phases) are all quite similar and may even be identical. It thus appears that the induced motions, super-imposed upon the several intrinsic ones by the perturbing intermolecular interactions, have a property of similarity independent of the differing natures of the intrinsic motions that are being perturbed.