Theories of Unimolecular Reactions

Slater N B 1959 Theory of Unimolecular Reactions (Wnaca, NY Cornell University Press)... 

Bunker D L and Pattengill M 1968 Monte Carlo calculations. VI. A re-evaluation of the RRKM theory of unimolecular reaction rates J. Chem. Phys. 48 772-6... 

Forst W 1973 Theory of Unimolecular Reaction. (Htvi York Academic)... 

Collisional energy transfer in molecules is a field in itself and is of relevance for kinetic theory (chapter A3.1). gas phase kmetics (chapter A3.4). RRKM theory (chapter A3.12). the theory of unimolecular reactions in general,... 

Quack M 1978 Theory of unimolecular reactions induced by monochromatic infrared radiation J. Chem. Phys. 69 1282-307... 

Slater, N. B. Theory of Unimolecular Reactions Cornell University Press Ithaca, NY, 1973. 

Forst, W. Theory of Unimolecular Reactions Academic Press New York, 1973. 

The notion of a collision implies at least two collision partners, but collision-based theories are applicable for theories of unimolecular reactions as well. 

The theory of unimolecular reactions is that the specific rate, k, depends on the pressure as... 

Pritchard, H. O. The quantum theory of unimolecular reactions, Cambridge University Press, Cambridge, 1984... 

In a series of important papers Marcus and coworkers applied the RRKM (Rice-Ramsberger-Kassel-Marcus) theory of unimolecular reactions to the ozone problem in a successful effort to rationalize the MIF s described above (see Historical Vignette 14.1). The 2002 paper of Gao and Marcus (reading list) considered a kinetic scheme which mildly elaborates that of Equation 14.1... 

Much of the recent work on the cyclopropane-propylene isomerization has had one of two objectives, either to try and determine which of the two reaction paths suggested by the early workers is involved, or to test the various theories of unimolecular reactions. Comer and Pease (1945), using catalytic hydrogenation to analyse their reaction product, but otherwise working under similar conditions to Chambers and Kistiakow-sky, suggested that all the results obtained could be represented just as well by the reaction scheme... 

Pritchard et al. (1953), using an improved analjdiical technique, were able to study the reaction down to a pressure of less than 0-1 mm (where the rate constant is only 10 % of the high-pressure value). Their results indicated quite clearly that the reaction was unimolecular, and in the pressure region, where the rate constant had decreased appreciably addition of inert gases did lead to an increase in rate. At the same time. Slater (1953) applied his theory of unimolecular reactions to this isomerization. 

The quasi-equilibrium theory (QET) of mass spectra is a theoretical approach to describe the unimolecular decompositions of ions and hence their mass spectra. [12-14,14] QET has been developed as an adaptation of Rice-Ramsperger-Marcus-Kassel (RRKM) theory to fit the conditions of mass spectrometry and it represents a landmark in the theory of mass spectra. [11] In the mass spectrometer almost all processes occur under high vacuum conditions, i.e., in the highly diluted gas phase, and one has to become aware of the differences to chemical reactions in the condensed phase as they are usually carried out in the laboratory. [15,16] Consequently, bimolecular reactions are rare and the chemistry in a mass spectrometer is rather the chemistry of isolated ions in the gas phase. Isolated ions are not in thermal equilibrium with their surroundings as assumed by RRKM theory. Instead, to be isolated in the gas phase means for an ion that it may only internally redistribute energy and that it may only undergo unimolecular reactions such as isomerization or dissociation. This is why the theory of unimolecular reactions plays an important role in mass spectrometry. 

Robinson, P. J. Holbrook, K. A. Unimolecular Reactions, Wiley-Interscience New York, 1972. Forst, W. Theory of Unimolecular Reactions, Academic New York, 1973. 

Thus transition-state theory provides a relatively straightforward way of estimating Aoo if it is unavailable from experiment. The next section treats the theory of unimolecular reactions, and in particular, their pressure dependence, much more rigorously. 

The Hinshelwood model thus corrects one of the major deficiencies in the Lindemann theory of unimolecular reactions. The greater excitation rate constant of Eq. 10.132 brings the predicted fall-off concentration [M]j/2 of Eq. 10.109 into much better accord with experiment. However, because of the many simplifying assumptions invoked in the Hinshelwood model, there are still a number of shortcomings. 

Rice, Ramsperger, and Kassel [206,333,334] developed further refinements in the theory of unimolecular reactions in what is known as RRK theory. Kassel extended the model to account for quantum effects [207] this treatment is known as QRRK theory. 

The modem theory theory of unimolecular reactions was established by Marcus, who built upon QRRK theory [260,261,431]. This work is known as the RRKM theory. We will... 

Derive an expression for the decomposition rate constant kd (e ) for the Hinshelwood theory of unimolecular reactions. 

R.G. Gilbert and S.C. Smith. Theory of Unimolecular Reactions. Blackwell Scientific, Oxford, 1990. 

N.B. Slater, Theory of Unimolecular Reactions (Cornell University Press, Ithaca, NY 1959) K.J. Laidler, op. cit. 

The theory of unimolecular reactions was at first based upon very scanty data and, until more experimental evidence was forthcoming, discussion of the mechanism tended to be a little unsatisfactory and inconclusive. The great theoretical interest of these changes will be made evident if we consider in turn the various theories about them which have been current. 

Before leaving general theoretical considerations we must briefly examine the consequences of the simple radiation theory of unimolecular reactions. The only unimolecular reactions to which, on purely a priori grounds, it would be necessary to apply this theory would be those in which the value of the velocity constant showed no diminution whatever as the concentration was indefinitely decreased. 

---