Time scale longest

The excited states used as the photoreductant in the CoPc are difficult to determine. No long-lived excited state is known for CoPc, and, therefore, we are unable to identify the states involved in the electron transfer reaction. The longest living excited state in CoPc is expected to have a life time on the neuiosecond time scale by analogy with other first row (open shell) transition metal phthalocyanines (33). 

A surprising aspect of SD is how rapidly C i) in highly polar solvents decays relative to other relaxation processes such as reorientation of solvent dipoles. This very rapid time scale cannot be ascribed to dynamical solvent-solvent correlations, which, as illustrated in Fig. 6, are modest even for the longest ranged A . Thus the key to imderstanding the reasons for the rapid decay of C i) is in examining how solvent-solvent correlations contribute to it and to what extent their contributions can be accounted for in terms of static correlations measured by ((5A ) ), Eq. (32). The initial cmvature of C(t), which characterizes its short-time Gaussian-like behavior is often characterized in terms of the solvation frequency co o/v... 

Our experiments and numerical simulations have proven that interference between chromophore and solvent responses greatly obscures the experimental observables in IR spectroscopy on water at waiting times >0.5 ps. However, the water dynamics can still be obtained if the thermal effects are carefully characterized and self-consistently included in the model. This results in the longest time scale for the frequency correlation function of 700 fs. 

This is possible when one has widely separated time scales such that the relaxation time is by far the longest characteristic time involved in the time evolution of the system. 

The transition from Eq. (38) to Eq. (40) is only possible if the relaxation process still corresponds to the longest relevant time scale in the system. 

Obviously, the various electronically excited states of an atomic or molecular ion vary in their respective radiative lifetime, t. The probability distribution applicable to formation of such states is thus a function of the time that elapses following ionization. Ions in metastable states, which have no allowed transitions to the ground state, are most likely to contribute to ion-neutral interactions observed under any experimental conditions since these states have the longest lifetimes. In addition, the experimental time scale of a particular experiment may favor some states over others. In single-source experiments, short-lived excited states may be of greater relative importance than in ion-beam experiments, in which there is typically a time interval of a few microseconds between ion formation and the collision of that ion with a neutral species, so that most of the short-lived states will have decayed before collision. There are several recent compilations of lifetimes of excited ionic states.lh,20 ,2,... 

If a mixer is to be used for reactive processes, it should be designed such that the longest mixing time scale (whether micro-, meso-, or macromixing) is significantly shorter than the characteristic time scale of the desired chemical reaction. As mentioned in Section 3, any of the time scales can be rate determining. 

The product r o is the characteristic relaxation time xq of the terminal region. In terms of molecular models, this time scales as the longest relaxation time. In terms of the distribution of relaxation times H(x), Xo is the "weight-average relaxation time" which is the average relaxation time related to the second order moment of the relaxation spectrum ... 

All dynamic events are not so rapid, however. Lipid flip-flop, in which a lipid translocates from one leaflet to another in a membrane, is usually a profoundly slow process and occurs in a time scale of minutes or even hours. As for the longest time scale associated with biological lipid systems, the typical life time of a cell ranges from a few days to several months, which depends on the tissue type. 

As discussed in the Introduction, CO2 exchange with the mantle becomes important on Earth s longest time scales. We consider in detail two sources (arc volcanoes and the mid-ocean ridge) and one sink (subduction of carbonitized basalts). 

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