Vibrational frequencies, distribution

The correlation of the vibrational frequency distributions of two modes can be determined from 2D-IR experiments and such effects are particularly evident in dual frequency experiments. For example, positive correlations between the amide-A and amide-I frequencies apparent from the spectra of acylalaninemethoxide (AcAlaOMe) in Figure 5, imply that when... 

S. Gnanakaran and R. M. Hochstrasser (2001) Conformational preferences and vibrational frequency distributions of short peptides in relation to multidimensional infrared spectroscopy. J. Am. Chem. Soc. 123, p. 12886... 

XVII. THE EFFECT OF CORRELATION OF VIBRATIONAL FREQUENCY DISTRIBUTIONS... 

D.K. Ross, P.F. Martin, W.A. Oates R. Khoda Bakhsh (1979). Z. Phys. Chem., 114, 221-30. Inelastic neutron scattering measurements of optical vibration frequency distribution in hydrogen-metal systems. 

Figure 3b. Bom-oon Kdrmdn vibrational frequency distribution for the LiF lattice ( ) and for the L F lattice (—) calculated with O K input data. The line.occurs in the region...

The vibrational frequency distribution can be obtained from the TOF spectra by an extrapolation procedure. This is fully justified when the scattering is predominantly incoherent, as is the case for metal hydrides. 

To characterize the ensemble-averaged vibrational frequency distribution, the vibrational INM density of states (DOS) are defined as follows ... 

Myers A B, Tchenio P and Moerner W E 1994 Vibronic spectroscopy of single molecules exploring electronic-vibrational frequency correlations within an inhomogeneous distribution J. Lumin. 58 161-7... 

At low enough temperatures, only that substitutional isomer which has the lowest ZPVE will be populated. At higher temperatures, however, other isomers may also be found, so that a superposition of several spectra is observed in an ESR experiment. Previously, we have found [1-4] that the abundances of these other isomers are well predicted by a Boltzmann distribution based on the differences in ZPVE. Since the 6-31G(d) and 6-31 lG(d,p) basis sets gave very similar geometries in the present case (see below), the vibrational frequencies and ZPVE for the mono-deuterated isomers were calculated only at the B3-LYP/6-31G(d) level. 

Intermediate Isotope distribution Vibration frequencies/cm Bond angle/ degrees... 

Pure rotational spectra only appear for molecules with permanent dipole moments and vibrational spectra require a change of dipole during the motion. However, electronic spectra are observed for all molecules, and changes in the electron distribution in a molecule are always accompanied by dipole changes. As a result even homonuclear molecules (H2 or N2) which have no rotation or vibration spectra, do give electronic spectra with vibrational and rotational structure from which rotational constants and bond vibration frequencies may be derived. 

The VEP-atomized particles are spherical. The mass median diameter of the particles ranges typically from 300 to 500 pm. Both the mass median diameter and size range of the particles reduce with decreasing wire diameter for a given vibration frequency. The narrowest particle size distribution is produced at the resonant... 

Vibrational spectroscopy can help us escape from this predicament due to the exquisite sensitivity of vibrational frequencies, particularly of the OH stretch, to local molecular environments. Thus, very roughly, one can think of the infrared or Raman spectrum of liquid water as reflecting the distribution of vibrational frequencies sampled by the ensemble of molecules, which reflects the distribution of local molecular environments. This picture is oversimplified, in part as a result of the phenomenon of motional narrowing The vibrational frequencies fluctuate in time (as local molecular environments rearrange), which causes the line shape to be narrower than the distribution of frequencies [3]. Thus in principle, in addition to information about liquid structure, one can obtain information about molecular dynamics from vibrational line shapes. In practice, however, it is often hard to extract this information. Recent and important advances in ultrafast vibrational spectroscopy provide much more useful methods for probing dynamic frequency fluctuations, a process often referred to as spectral diffusion. Ultrafast vibrational spectroscopy of water has also been used to probe molecular rotation and vibrational energy relaxation. The latter process, while fundamental and important, will not be discussed in this chapter, but instead will be covered in a separate review [4],... 

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