Chemical unimolecular

Chain uncoiling, and the converse process of coiling, is conveniently considered as a unimolecular chemical reaction. It is assumed that the rate of uncoiling at any time after application of a stress is proportional to the molecules still coiled. The deformation Dhe(0 at tinie t after application of stress can be shown to be related to the equilibrium deformation Dhe( ) by the equation... 

As in a unimolecular chemical reaction, the rate law for nuclear decay is first order. That is, the relation between the rate of decay and the number N of radioactive nuclei present is given by the law of radioactive decay ... 

DISCUSSION AND CONCLUSIONS In this study a general applicable model has been developed which can predict mass and heat transfer fluxes through a vapour/gas-liquid interface in case a chemical reaction occurs in the liquid phase. In this model the Maxwell-Stefan theory has been used to describe the transport of mass and heat. A film model has been adopted which postulates the existence of a well-mixed bulk and stagnant zones where the principal mass and heat transfer resistances are situated. Due to the mathematical complexity the equations have been solved numerically by a finite-difference technique. In this paper (Part I) the Maxwell-Stefan theory has been compared with the classical theory due to Pick for isothermal absorption of a pure gas A in a solvent containing component B. Component A is allowed to react by a unimolecular chemical reaction or by a bimolecular chemical reaction with... 

NONEQUILIBRIUM THERMODYNAMICS A PRIMER UNIMOLECULAR CHEMICAL KINETICS MOLECULARITY ORDER OF REACTION ELEMENTARY REACTIONS Unimolecular forward/bimolecular reverse, CHEMICAL KINETICS Unimolecular isomerization,... 

The surface reaction rate is assumed to be a unimolecular chemical reaction AS — B S, which has the rate expression... 

In most of studies so far (e.xperimenlal as well as theoretical) on the condensation coefficient o, the condensation process has been considered as a unimolecular chemical reaction, which means that the evaluation of o is eciuivalent to estimating how many vapor molecules are reflected after colliding with the liquid surface. In order to avoid confusion, let Oseir be the condensation coelficient from this point of view, since we show later that the assumption of the unimolecular reaction is not always correct. 

In principle, we can evaluate Os if by direct counting of collision and reflection events from the molecidar trajectory data for both cases, we observed sufficient number (about 200) of collision events. To estimate Os,.if quantitatively, we have developed an autocorrelation function method. The result is Oseif —90% and there is no qualitative difference among various types of fluids, which suggests that the condensation as a unimolecular chemical reaction is a barricrless process. Calcidation of the local chemical potential also supports this barrieijess picture. ... 

The apparent equilibrium constant for this unimolecular chemical reaction is... 

The relation between the amount, x, of a substance transformed at the time, t, in a unimolecular chemical reaction may be written x=a( 1 -e kt) where a denotes the amount of substance present at the beginning of the reaction, and A is a constant. Show that V = ake lct or, V = k(a - x) according as we refer the velocity to equal intervals of time, t or to equal amounts of substance transformed, x. Also show that the mean velocity with respect to equal intervals of time in the interval - t0i is... 

In a unimolecular chemical reaction, the molecule acquires the necessary energy to become activated and then decomposes. The majority of reactions involve only union bimolecular steps. The following reactions are all unimolecular ... 

Assuming that the concept of a rate constant is valid, we might consider using a microscopic theory of unimolecular chemical reactions to predict what the reaction rate should be and then check to see whether the theory is in agreement with that obtained from the computer simulation. The theory most widely used for this purpose is the RRKM theory developed by Rice and Ramsperger,36 Kassel,and Marcus and co-workers. As has been discussed in detail elsewhere,RRKM theory contains the same essential dynamical assumptions contained in transition-state theory. We discuss these assumptions briefly in the next section. 

All non-radiative electronic processes are isoenergetic transitions to another electronic state, which may or may not be the ground state. This other state may be localised on the same molecule, or on molecules produced by unimolecular chemical reaction from the excited-state or the process may involve interaction with states on another system which acts as a quencher of the excited-state, e.g. by energy transfer or bimolecular reaction. (The resultant electronic state(s) may themselves deactivate non-radiatively or radiatively, e.g. the phosphorescence from a triplet state formed from a higher singlet, emission from excimers and exciplexes formed from ground-state excited state interaction (see Sect 1.13.5.5), or emission from quencher states produced by energy transfer or chemical reaction.)... 

Table 3. Unimolecular chemical reactions of solutes in liquid crystalline solvents...

Consider a system with a bistable free energy F q) as shown in Fig. 3. Such a free energy might be characteristic for a molecule in solntion undergoing isomerizations between two stable conformations A and B, i.e., for a unimolecular chemical reaction... 

K. V. Reddy and M. J. Berry, A nonstatistical unimolecular chemical reaction Isomerization of state-selected allyl isocyanide, Chem. Phys. Lett. 66 223 (1979). 

The problems in analyzing the results of photochemical (and chemical) activation experiments on unimolecular reactions (see Section 1.4) are closely related to those which arise in studies of fluorescence quenching. Excitation of a polyatomic molecule with monochromatic radiation can produce species with a well-defined energy (e) which exceeds the critical energy (e°) for some unimolecular chemical change. The usual goal in such experiments is to find the specific rate constant, k e defined by... 

In this chapter we describe the estimation and interpretation of rate coefficients for thermal dissociation, isomerization, and recombination reactions. While such reactions are only a small fraction of the elementary reactions of combustion mechanisms, some of them do play essential roles. Their kinetic behavior is governed by the competition of unimolecular chemical changes in molecular structure with bimolecular physical collisional energization and deenergization processes. 

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