Intramolecular transfer of vibrational energy

It was pointed out in Section 4.2 that most polyatomic molecules show only a single relaxation process, owing to rapid intramolecular vibration-vibration transfer between modes. This corresponds to a state of affairs where Vibrational energy enters the molecule via process (a), which is rate-determining, 

For a few polyatomic molecules, where there is a large difference between Vj and v2, the rate of the complex process (c) is much slower, and the condition P2 P12 Pi applies. This gives rise to a double relaxation phenomenon. Process (b) is again too slow to play any role, but process (a) is now faster than process (c). The vibrational energy of mode 2 (and any upper modes) relaxes 

EXPERIMENTAL COLLISION NUMBERS FOR INTRAMOLECULAR VIBRATIONAL ENERGY 

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Rice S A 1981 An overview of the dynamics of intramolecular transfer of vibrational energy Adv. Chem. Phys. 47 117-200... 

Rice, S. A. (1981), Overview of the Dynamics of Intramolecular Transfer of Vibrational Energy, Adv. Chem. Phys. 47, 117. 

S. A. Rice, Overview of the dynamics of intramolecular transfer of vibrational energy, Adv. Chem. Phys. 47 117 (1981) P. Brumer, Intramolecular energy transfer theory for the onset of statistical behavior, Adv. Chem. Phys. 47 202 (1981) P. Brumer and M. Shapiro, Chaos and reaction dynamics, Adv. Chem. Phys. 70 365 (1988). 

Seilmeier A and Kaiser W 1988 Ultrashort intramolecular and intennolecular vibrational energy transfer of polyatomic molecules in liquids Ultrashort Laser Pulses and Applications (Topics in Applied Physics 60) ed W Kaiser (Berlin Springer) pp 279-315... 

Vibrational Predissociation, in this section we discuss the case of a transition from a predissociative state to the photofragment state that occurs on a single adiabatic pes. Such processes cannot occur for diatomic molecules, but they can be observed for polyatomic systems. The transition is caused by intramolecular energy transfer, that is, by internal redistribution of vibrational energy. 

Seihneier A, Kaiser W. Ultrashort intramolecular and intermolecular vibrational energy transfer of polyatomic molecules in liquids. In Kaiser W, ed. Ultrashort Laser Pulses and Applications. Vol. 60. Berlin Springer-Verlag, 1988 279-315. 

Slater [13] has criticized the RRKM theory, mainly on the grounds that the proposed model assumes that the intramolecular transfer of energy between vibrational degrees of freedom is very rapid compared to the rate of reaction. In fact, all theories of unimolecular reactions, aside from Slater s, involve this particular assumption. Slater assumes that the rate of intramolecular vibrational-energy transfer is very slow. He then performs a normal-mode analysis of the reacting molecule, assuming that reaction occurs when the bond to be broken reaches a certain critical length. A formally correct expression for is obtained, namely. 

Fig. 13.16a,b. Fluorescence detection of vibrational energy transfer from an optically pumped molecular level (a) intermolecular transfer HF -> CO, N2. The mean numbers of collisions are given for the different collision-induced transitions, (b) Intramolecular transfer CH (v3) CH (v2) + A kin [13.77]... 

A. Seilmeier, W. Kaiser Ultrashort Intramolecular and Intermolecular Vibrational Energy Transfer of Polyatomic Molecules in Liquids, in W. Kaiser (ed.) Ultrashort Laser Pulses and Applications, Springer, Berlin, p. 279 (1988)... 

This is no longer the case when (iii) motion along the reaction patir occurs on a time scale comparable to other relaxation times of the solute or the solvent, i.e. the system is partially non-relaxed. In this situation dynamic effects have to be taken into account explicitly, such as solvent-assisted intramolecular vibrational energy redistribution (IVR) in the solute, solvent-induced electronic surface hopping, dephasing, solute-solvent energy transfer, dynamic caging, rotational relaxation, or solvent dielectric and momentum relaxation. 

Uzer T 1991 Theories of intramolecular vibrational energy transfer Rhys. Rep. 199 73-146... 

T. Uzer, Phys. Rep., 199, 73 (1991). Theories of Intramolecular Vibrational Energy Transfer. 

Desorption can proceed via several mechanisms. For solids with a negative electron alSnity such as Ar [49,149-151] and N2 [153], the extended electron cloud around a metastable center will interact repulsively with the surrounding medium and metastables formed at the film-vacuum interface will be expelled into vacuum (the so-called cavity expulsion mechanism [161]). Also permitted in solids with positive electron affinities (e.g., CO) is the transfer of energy intramolecular vibration to the molecule-surface bond with the resulting desorption of a molecule in lower vibrational level [153,155,158-160]. Desorption of metastables via the excitation of dissociative molecular (or excimer) electronic states is also possible [49,149-151,154,156,157]. A concise review of the topic can be found in Ref. 162. 

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