Dephasing rate

I CRS interferogram with a frequency of A = coj + 2c0j - cOq, where cOp is the detected frequency, coj is the narrowband frequency and coj the Raman (vibrational) frequency. Since cOq and coj are known, Wj may be extracted from the experimentally measured RDOs. Furthemiore, the dephasing rate constant, yj, is detemiined from the observed decay rate constant, y, of the I CRS interferogram. Typically for the I CRS signal coq A 0. That is, the RDOs represent strongly down-converted (even to zero... 

Hence the dephasing rate is directly proportional to the rotational relaxation rate 1/xj, while w0 in (3.23) is inversely proportional to it. 

From Eqs (7.5) and (7.6) we can deduce that the pure dephasing rate is Yio( ) = 0.2ps 1 and the vibrational relaxation takes place in the timescale of 0.5 ps for the 100-cm 1 mode. More results related to vibrational relaxation have been reported by Martin group [1-5], In this chapter we choose 0.3 ps for the 100-cm-1 mode, and the vibrational relaxation rates for other modes are scaled with their vibrational frequencies. 

In a heavy fermion compound Yb MnSbn, the dephasing rate of the coherent optical phonons decreased with lowering temperature above Curie temperature Tc, but increased below Tc- The results were attributed to the coupling between an optical phonon mode and the Kondo effect [100]. 

Fig. 3. Above, plots of PE and RTG signals for propane (250torr) showing similar exponential decays. Below, plots of dephasing rate versus number density of the buffer gas propane for both PE and RTG experiments.

Plots of dephasing rate versus buffer gas pressure allow us to extract homogeneous dephasing cross sections according to equation (2). In Fig. 3 (bottom) we show Iodine coherence dephasing data for propane buffer gas. Note the similarity of the extracted cross sections in both the PE and RTG cases. These measurements were repeated for a series of buffer gases and the results are contained in Table l.[3]... 

The observations of vibrational coherence in optically initiated reactions described above clearly show that the standard assumption of condensed-phase rate theories—that there is a clear time scale separation between vibrational dephasing and the nonadiabatic transition—is clearly violated in these cases. The observation of vibrational beats has generally been taken to imply that vibrational energy relaxation is slow. This viewpoint is based on the optical Bloch equations applied to two-level systems. In this model, the total dephasing rate is given by... 

G. R. Fleming An interesting feature of the Redfield theory calculations is that attempts to stop coherence transfer by increasing the dephasing rate also increases the coherence transfer rate. In addition, two-state calculations [M. Jean and G. R. Fleming, J. Chem. Phys. 103, 2092 (1995)] show that the coherence transfer can survive reasonable amounts of anharmonicity. It appears to be quite robust. 

However, none of the above-mentioned theories can satisfactorily explain the observed nonquadratic quantum number dependence of the dephasing rate. That the situation is somewhat complex can be understood from the following analysis. The average dephasing time (t ) is given by [125]... 

The overtone dephasing rates are found to be substantially subquadratic in n dependence and show good qualitative agreement with the experimental observations and also computer simulation studies [133]. For higher levels (n > 4), a linear dependence on n was obtained. This linear dependence of the dephasing rate on the quantum number n has a simple physical explanation. As n increases, the dephasing becomes faster and is determined mainly by the initial fast dynamics of the liquid. This naturally leads to a linear dependence on n for large n. 

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