Rate constant internal conversion

Rate constant for internal conversion Rate constant for intersystem crossing Rate constant for non-radiative decay Observed decay rate constant... 

The fact that the internal-conversion rate remains constant up to about 1 mole per cent suggests that perhaps this is the concentration at which the terbiums attain a close enough spacing to be first considered as pairs. 

Quenching rate constants for dienes and quadricyclenes have similar sensitivities to the electronic and structural features of the excited aromatic hydrocarbon. However, during this process quadricyclene isomerizes to nor-boraadiene with a quantum yield of 0.52, whereas dienes usually remain unchanged/10 Hammond has suggested that vibrational energy which is partitioned to the acceptor upon internal conversion of the exciplex can lead to isomerization(10a,103) ... 

From the above discussion, we can see that the purpose of this paper is to present a microscopic model that can analyze the absorption spectra, describe internal conversion, photoinduced ET, and energy transfer in the ps and sub-ps range, and construct the fs time-resolved profiles or spectra, as well as other fs time-resolved experiments. We shall show that in the sub-ps range, the system is best described by the Hamiltonian with various electronic interactions, because when the timescale is ultrashort, all the rate constants lose their meaning. Needless to say, the microscopic approach presented in this paper can be used for other ultrafast phenomena of complicated systems. In particular, we will show how one can prepare a vibronic model based on the adiabatic approximation and show how the spectroscopic properties are mapped onto the resulting model Hamiltonian. We will also show how the resulting model Hamiltonian can be used, with time-resolved spectroscopic data, to obtain internal... 

The rate constant ke corresponds to the reciprocal of the lifetime of the excited state. Internal conversion The excited state can do other things, such as convert some of the original electronic excitation to a mixture of vibration and a different electronic state. These are also treated as unimolecular processes with associated rate constants ... 

The preferred general method is the vacuum reaction calorimeter because of its wide range and flexibility, and because the enthalpy of the reactions is a good indicator of whether a polymerisation has gone to completion in any case, tests for residual monomer by glc must not be omitted. The complete reaction curve, however acquired, can reveal not only the internal order of a reaction, and whether it changes with conversion, and it is a far firmer base for calculating rate-constants than the initial rate or a maximum rate. 

All reactions at 19 °C, 0 °C, and -19 °C were of the first order internally, up to at least 90% conversion, and all went to completion. Details are given in Tables 1-3. The first-order rate constant, kt, is directly proportional to the acid concentration as shown by the constancy of the values of kp = 1/[HClO4]0. The Arrhenius plot for kp gave... 

The competing intramolecular photophysical processes that can occur from Si(v0) are fluorescence, intersystem crossing and internal conversion, with first-order rate constants of kf, kisc and kic, respectively (Figure 3.3). 

Using the values of quantum yields and fluorescence lifetime, rate constants on the state were obtained. The results are summarized in "Table III". As seen in "Table III", no isotope effect is observed in the rate constants for the fluorescence and intersystem crossing. On the other hand, in the case of TPP the rate constants of internal conversion show a large isotope effect that of D2TPP is... 

Table III. Rate Constants of Fluorescence (k ), Intersystem Crossing (kj g ), and Internal Conversion (kj )...

While in the case of OEP, the rate constant of the internal conversion for D2OEP was about one-half that of H2OEP as shown in "Table III". There is not such a marked isotope effect as in the case of TPP but a slight isotope effect can be observed. So, we can conclude that N-H vibrations may play an important role in internal conversion in OEP. The deuterated OEP at meso positions (OEP-d )... 

Table 7 Properties of t-Sf, c-Sf, and DPCB in the D2 State Lifetime (r), Rate Constants for Internal Conversion (fc c), c-t Isomerization (k ), and Product Formation (kp), and Excitation Energy ( ex)...

The radiationless transitions are indicated by wavy lines with the corresponding rate constants or lifetimes. The rates of thermalization of a dye molecule after an absorptive or emissive transition, namely k in the excited singlet state Si and k" in the ground state So, axe so fast that they have not yet been reliably measured. From indirect evidence they are believed to be k k" rs 1012 — 1013 sec-1. The rate 21 °f radiationless internal conversion from S2 to Si has recently been measured for several dyes and was found to be in the range kzi = 1011 —1012 sec-1 5>6 While has not yet been measured directly, there is no reason to believe that it should be much different from A 21, and indirect evidence seems to... 

Fig. 14. Schematic representation of energy levels and transitions for fluorescence and related processes kic, rate constant for interval conversion fcF, rate constant for fluorescence fcISC, rate constant for intersystems crossing fc[cp> rate constant for internal conversion from triplet state kp, rate constant for phosphorescence S, energy level for the first excited singlet state after solvent rearrangement for a polarity probe in a polar solvent.

The rates of internal conversion from the 5Z)3 to the 5D4 states were also measured. The backup oxide in this case was yttrium. This information was obtained by determining the rise time of the 5Z)4-state green fluorescence as a function of time, when the 5Z>3 state was excited. The rise time of the 5Z)4 state is, of course, the decay time of the 5Z>3 state. It was assumed that the decay of the 5Z)3 was predominantly due to an efficient internal conversion process to the 5D4. Measurements of the decay time of the 5Z)3 state directly were not possible, since the emission from this state is very weak if not, indeed, absent. The result of this study is shown in Fig. 23, where it can be seen that the internal-conversion time remains constant at about 17 fxsec up to a terbium oxide concentration of 1 mole per cent. At higher concentrations, the internal conversion time falls rapidly, until at 10 mole per cent terbium oxide the value is about 1.7 /xsec. This is down by a factor of 10 over samples containing 1 mole per cent or less of terbium oxide. 

From kinetic considerations each can be further subdivided according to observed values of rate constants fcIC, the rate constant for internal conversion and kIsc, the rate constant for intersystem crossing. 

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