High-frequency, limiting-phonon

In the time-domain detection of the vibrational coherence, the high-wavenumber limit of the spectral range is determined by the time width of the pump and probe pulses. Actually, the highest-wavenumber band identified in the time-domain fourth-order coherent Raman spectrum is the phonon band of Ti02 at 826 cm. Direct observation of a frequency-domain spectrum is free from the high-wavenum-ber limit. On the other hand, the narrow-bandwidth, picosecond light pulse will be less intense than the femtosecond pulse that is used in the time-domain method and may cause a problem in detecting weak fourth-order responses. 

The similarity between the A C o spectra doped with different alkali metals again indicates that the observed modes are due only to the Cfio molecule, and that there are no observable A-Cfto modes above 100 cm The mode at 270 cm has a resolution-limited FWHM for CSftCfio, is broadened in nd is a doublet in K C q. The high-frequency mode of the doublet may result from a two-phonon process involving a low cnergy-A-Cfrequency modes (1383 cm and 1478 cm ). If this is the case, it is not clear that these modes should be broadened in the same way as the... 

The phonon frequencies Vpho on in proteins have the following characteristic values at acoustic modes they lie between 10" and 10" s" ( 0.0004-0.004 eV) in a polypeptide chain the acoustic modes are generated by vibrations, which cause changes in the relative distances and orientations of the side chains. The upper limit is given by the high-frequency intramolecular vibrational modes of hydrogen atoms with a frequency of 10 s" ( 0.4 eV). At body temperatures (k T ks 310 K 0.03 eV), the acoustic modes will be most active in the scattering of electrons. Therefore for the subsequent considerations Vphonon = 10 s has been taken as the characteristic value. 

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