Anti Stokes line

The next two temis (Lorentzians) arise from the mechanical part of the density fluctuations, the pressure fluctuations at constant entropy. These are the adiabatic sound modes (l/y)exp[-FA t ]cos[co(A) t ] with (D(k) = ck, and lead to the two spectral lines (Lorentzians) which are shifted in frequency by -ck (Stokes line) and +ck (anti-Stokes line). These are known as the Brillouin-Mandehtarn, doublet. The half-width at... 

Antistatic coatings Antistatic finishes Antistatic yarns Antistatin D Antisterility vitamin Antistick agents Antistick applications Anti-Stokes lines... 

The third common level is often invoked in simplified interpretations of the quantum mechanical theory. In this simplified interpretation, the Raman spectrum is seen as a photon absorption-photon emission process. A molecule in a lower level k absorbs a photon of incident radiation and undergoes a transition to the third common level r. The molecules in r return instantaneously to a lower level n emitting light of frequency differing from the laser frequency by —>< . This is the frequency for the Stokes process. The frequency for the anti-Stokes process would be + < . As the population of an upper level n is less than level k the intensity of the Stokes lines would be expected to be greater than the intensity of the anti-Stokes lines. This approach is inconsistent with the quantum mechanical treatment in which the third common level is introduced as a mathematical expedient and is not involved directly in the scattering process (9). 

The energy of the scattered radiation is less than that of the incident radiation for the Stokes line of the Raman spectrum and the energy of the scattered radiation is more than that of the incident radiation for the anti-Stokes line. The energy increase or decrease from the excitation is related to the vibrational energy spacing... 

Figure 3.6. A simplified energy diagram illustrating the origins of Rayleigh scattering and of the Stokes and anti-Stokes lines in the Raman spectrum.

Figure 2.52 Schematic representation of the transitions giving rise to the Raman effect. GS = ground electronic state, ES = excited electronic state, VS = virtual electronic stale, R = Rayleigh scattering, S = transitions giving rise to Stokes lines, AS = transitions giving rise to Anti-Stokes lines, RRS = transitions giving rise to resonance Raman.

Figure 3. Energy schemata of transitions involving vibrational states (a excitation of 1st vibrational state - mid-IR absorption b excitation of overtone vibrations - near-IR absorptions c elastic scattering - Rayleigh lines d Raman scattering - Stokes lines e Raman scattering - Anti-Stokes lines f fluorescence).

Through interaction of the Stokes lines with the laser line, stimulated anti-stokes lines can be produced 223),... 

Higher order Stokes or anti-Stokes lines have been observed to occur at exact harmonics of the first vibrational 724) or rotational 723) shifts. 

Occasionally absorption occurs from a higher vibrational level of S0. This leads to anti-Stokes lines, in which the fluorescence is at shorter wavelengths than... 

Symmetrically with respect to the Rayleigh line lie the somewhat less intense anti-Stokes lines which correspond to the transfer of energy from the molecule to... 

Section 2.3). The scattered light consists of two types one, called Rayleigh scattering, is strong and has the same frequency as the incident beam (vo), and the other, called Raman scattering, is very weak ( 10 5 of the incident beam) and has frequencies vo vm, where vm is a vibrational frequency of a molecule. The vo — vm and vo + vm lines are called the Stokes and anti-Stokes lines, respectively. Thus, in Raman spectroscopy, we measure the vibrational frequency (vm) as a shift from the incident beam frequency (vo). In contrast to IR spectra, Raman spectra are measured in the UV-visible region where the excitation as well as Raman lines appear. 

However, this equation is not applicable when anti-Stokes lines are very weak. It should be noted that these equations are applicable only for the spectra obtained under off-resonance conditions. For the spectra obtained under resonance conditions, see Ref. 66. 

---