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Thermal occupation

In several cases—such as, for example, phthalocyanine and protoporphyrin IX derivatives— the energy red shift and broadening of the transition with pressure may be sufficient to ensure a thermal population of the excited state, by occupation of a ti orbital. As discussed above, the thermal occupation of excited states may lead in principle to the formation of a reaction product. [Pg.164]

Ballard (4) points out that, below the energy of the band maximum, the photoemission current varies exponentially with photon energy, which is evidence that the band width is due to thermal occupation of vibrational levels in the electronic ground state, Fe(CN)64-(env). The threshold energy was found to be approximately 119 kcal mole 1 (4b) [118.3 kcal mole-1 by another method (7b)], i.e. about 18 kcal mole-1 lower than AL. It seems likely that the low-energy threshold of the spectrum represents emission from those Fe(CN)64- ions which happen to have solvent environments similar to those that characterize the ground state of Fe(CN)63-. [Pg.189]

Participation of low-frequency intermolecular vibrations in the fluctuation preparation of the barrier changes principally the mechanism of temperature dependence K T) compared to the one-dimensional tunneling model. According to relation (5), to the Arrhenius relationship there corresponds the predominance of thermally activated over-the-barrier transitions over the tunneling ones, which is determined in the harmonic terms model (Figure 1) by the thermal occupation of the highest vibrational sublevels of the initial... [Pg.384]

The result (13.61) has the characteristic fonn of a multiphonon relaxation rate that was already encountered in Chapter 12 (compare Eq. (12.55)). Note the appearance in this result of the important parameters that detennine this rate The coupling matrix element qjf between the tw o system states, the parameters (ya- that detennine the strength of the system-bath coupling, the energy gap a>j f between the two levels for which the transition is considered, the phonon frequencies and their thermal occupation numbers. Several more points are noteworthy ... [Pg.473]

The measurements discussed so far are not restricted to a particular selected state. Bennewitz et al. (1969) report measurements on CsF with the j = 1, ntj = 0 or the j = 2, rnj = 0 state being selected. Theoretically those states with the highest preferential orientation should be selected. More practical are considerations of thermal occupation numbers and easy focusability. It is more difficult to produce a pure beam of molecules in higher rotational states because the Stark effect of neighbouring states differs less and consequently their discrimination involves more effort. [Pg.401]

A notable measure of the intermolecular forces is the maximum frequency v of the lattice vibrations (optical phonons). In a typical organic molecular crystal, it is of the order of 3.5 THz in Si, in contrast, it is 14THz. Thus the difference in the Boltzmann factors exp(-hv/feT) for the thermal occupation of phonon states, which plays a decisive role in many solid-state properties, is already great when comparing organic and inorganic solids at room temperature, and it becomes very much greater at low temperatures (Table 1.2). [Pg.11]

The overall bandwidths are thus larger than feT for all the crystals W fegT For the transport properties, the thermal occupation of the bands must therefore be taken into account at 300 K and lower temperatures, only states in the neighbourhood of the band minima are occupied (cf Eq. (8.87)). [Pg.273]

CEF-level occupational numbers in the presence of a molecular field (or applied field) thermal occupation number of CEF -state I impurity concentration number of RE-ions electron density of states Stevens operators... [Pg.296]

In this calculation, the intensities of the spectral features have to be corrected by factors which account for the wavelength of the Rayleigh scattering in small particles and the thermal occupation of the phonon density of states. The equations do not include resonance effects therefore, the spectra have to be measured off-resonance [48]. [Pg.514]


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See also in sourсe #XX -- [ Pg.254 ]




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