Fragmentation time constant

Fig. 8. Computed T, versus P, (the probability of state 1) for the four DNA restriction fragments. Time constant for internal motion r, is 10 s.

Figure 20.5. A graphical representation of the time evolution of transients for the Norrish type-I a-cleavage 43 and 46 amu fragments from acetone and from acetone-de- The representative sets of data points ( for 43 amu, for 46 amu fragments) are modeled with simple buildup and decay response functions, I(t) = 4[exp(—t/t2) — exp(—f/x])] the time constants of buildup and decay are Ti and T2, respectively. A modest isotope effect on the characteristic time for formation of these acyl radicals (60 and 80 fs, respectively) and a more prominent —CH3/—CD3 effect on decays through loss of CO (420 and 670 fs, respectively) were recorded. ...

Due to the difference in the number of probe photons required to ionize the clusters from each state, careful study of the ion signal probe power dependence made it possible to determine the origin of each of the observed components. The X, X2 component is the result of the two photon excitation of the S02 F band. The X3 decay component is due to the one photon excitation of the coupled 1A2, Bi states. The plateau is believed to be due to ion-state fragmentation of larger clusters and does not seem to influence the values of the time constants obtained from the fitting procedure. 

If (5.27a) is fulfilled, propagate the trajectory in time until the interaction is zero and the internal energy of the fragment is constant. 

Zhao and Rice have calculated the fragmentation rate constant k by fitting the numerical simulation data from the time at which dissociation first starts to the time when... 

The systematically performed pump-probe spectroscopy on alkali clusters provided a good indication about suited candidates for a coherent control experiment. Among these, the fragmentation dynamics of the heteronu-clear trimer Na2K appeared to us the best. The corresponding pump-probe spectrum is shown in Fig. 14(a). It clearly exhibits — superimposed on an exponential decay with a time constant of 3.28 ps — an oscillatory behaviour with a period of roughly 500 fs. The Fourier-transform of this... 

Direct fragmentation of the clusters of interest excited by the pump pulse. This fragmentation process is identical to that of the simple decay model and is called Type I. Its time constant is given by ri. 

Increasing population due to fragmentation of larger clusters into the recorded mass channel with a decay constant r, followed by a re-fragmentation of these clusters with time constant T2 (Type II fragmentation)... 

To describe this more complicated behavior, the extended fragmentation model given in Sect. 2.2.2 is utilized as a basis. It takes into account the population density and fragmentation characteristics of Type I and Type II clusters. Since for delay times At < 0 and At > 0 the pump and probe pulses play different roles a further fragmentation channel has to be added to the extended model. Hence, the model used here contains four different fragmentation processes with four time constants tq, n, T2, and ts. Here, To characterizes the fragmentation behavior of the relevant Type I clusters. 

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