Energy accomodation

The quantity c is the condensation coefficient (of the order of unity) which describes the energy accomodation of the adsorbing species. The activation energy of adsorption is illustrated by the onedimensional adsorption potential shown in Fig. 3. 

In the case of incomplete accomodation the tempereture of diffusively desorbing particles T< would differ firom that of the surface T,. Energy accomodation coefficient as for such conditions is assumed to be of the form... 

The interaction potential is a damped exp-6 potential with parameters from ref. [40]. The force constant F was obtained from the Debye frequency corresponding to a Debye temperature 315 K. Energies in kJ/mol. a is the energy accomodation coefficient Ei ,/Ekin, where Eun is the initial kinetic energy. 

One possible explanation is that adamantyl cation, an intermediate in the reaction, is particularly unstable because it cannot accomodate a planar carbocation center (see Chapter 1, Problem 9). Examine the geometry of adamantyl cation. Does it incorporate a planar carbocation center Compare electrostatic potential maps of adamantyl cation and 2-methyl-2-propyl cation. Which cation better delocalizes the positive charge Assuming that the more delocalized cation is also the more stable cation, would you expect adamantyl tosylate to react slower or faster than tcrf-butyl tosylate Calculate the energy of the reaction. 

Another possible explanation is that 2-methyl-2-propyl cation allows better access to solvent than adamantyl cation. Examine hydrates of 2-methyl-2-propyl and adamantyl cations. How many water molecules does each accomodate Calculate hydration energies for the two cations. (The energy of water is provided at left.)... 

The competition between the polar and steric dipoles of molecules may also lead to internal frustration. In this case, the local energetically ideal configuration cannot be extended to the whole space, but tends to be accomodated by the appearance of a periodic array of defects. For example, the presence of the strong steric dipole at the head of a molecule forming bilayers will induce local curvature. As the size of the curved areas increases, an increase in the corresponding elastic energy makes energetically preferable the... 

In the case of ventilation consideration of energy conservation must be taken into account. Some work in recent years, however, indicate that the conflicting requirements of energy conservation by means of making dwellings more airtight and increased ventilation for radon reduction may be accomodated by the use of heat exchangers... 

Orbitals. Atomic orbitals represent the angular distribution of electron density about a nucleus. The shapes and energies of these amplitude probability functions are obtained as solutions to the Schrodinger wave equation. Corresponding to a given principal quantum number, for example n = 3, there are one 3s, three 3p and five 3d orbitals. The s orbitals are spherical, the p orbitals are dumb-bell shaped and the d orbitals crossed dumb-bell shaped. Each orbital can accomodate two electrons spinning in opposite directions, so that the d orbitals may contain up to ten electrons. 

We can also consider cases in which the intrinsic barrier is altered. Two such effects are steric hindrance and contribution of charge-separated structures to the transition state. Steric hindrance raises the energy of the transition state compared to that of a similarly exothermic unhindered model. This can be accomodated by considering an increase in the intrinsic barrier, which therefore makes the isotope effect rise. In ref.11 this is alternatively interpreted in a quadratic representation of the surface as an increase in the interaction force constant, and thus also correlated with an increase in the tunnel correction. An example of such an enhancement is the large value of the isotope effect in the trityl radical mesitylenethiol reaction in Table 1. 

The possibility of the deactivation at the reactor walls of vibrationally excited molecules was not considered. This contribution to the overall loss of excitation is determined by the accomodation coefficient for vibrational energy of the wall material and by the transport coefficients of the molecules to the walls. An example will serve for illustration The first order rate constant kw which accounts for the losses of vibrational excitation of an excited species at the reactor walls can be expressed as... 

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