Vibration, promoting

From (6.31) it follows that coupling contributes to the Fg potential, even if the latter term is absent from the bare potential. Both shaking and breathing vibrations promote tunneling, but in... 

One of the most significant recent insights in surface chemical dynamics is the idea that the principle of detailed balance may be used to infer the properties of a dissociative adsorption reaction from measurements on an associative desorption reaction.51,52 This means, for example, that the observation of vibrationally-excited desorption products is an indicator that the dissociative adsorption reaction must be vibrationally activated, or vice versa the observation of vibrationally-cold desorption products indicates little vibrational promotion of dissociative adsorption. In this spirit, it is... 

According to the Born-Oppenheimer approximation, the motions of electrons are much more rapid than those of the nuclei (i.e. the molecular vibrations). Promotion of an electron to an antibonding molecular orbital upon excitation takes about 10-15 s, which is very quick compared to the characteristic time for molecular vi-... 

From (7.32) it follows that coupling contributes to the V6 potential even if the latter term is absent in the bare potential U(d>). Both shaking and breathing vibration promote tunneling, but in a different way. Shaking makes the effective barrier narrower, while breathing lowers it. Similar to Section 4.2, we define a parameter that characterizes the relative modulation of the barrier by breathing modes (C = 0) ... 

In some host lattices emission has also been observed from the higher excited levels Ij, Dj, and even Gj (see above). In the case of borates and hydrates, however, all these emissions are quenched in favor of the Pj emission. This is a clear demonstration that higher-frequency vibrations promote the radiationless transitions to the Pj levels. 

Spectroscopy involves instrumental methods for determining the structure of organic compounds by measuring and interpreting their interaction with electromagnetic radiation. Radiation can cause a measurable transformation or pertubation in molecules such as molecular rotation, bond vibration, promotion of electrons to higher energy levels, or even permanent disruption of the molecule. 

Huang Y, Rettner CT, Auerbach DJ, Wodtke AM (2000) Vibrational promotion of electron transfer. Science 290 111... 

An alternative perspective is as follows. A 5-frmction pulse in time has an infinitely broad frequency range. Thus, the pulse promotes transitions to all the excited-state vibrational eigenstates having good overlap (Franck-Condon factors) with the initial vibrational state. The pulse, by virtue of its coherence, in fact prepares a coherent superposition of all these excited-state vibrational eigenstates. From the earlier sections, we know that each of these eigenstates evolves with a different time-dependent phase factor, leading to coherent spatial translation of the wavepacket. 

Figure Al.6.8. Wavepacket interferometry. The interference contribution to the exeited-state fluoreseenee of I2 as a fiinotion of the time delay between a pair of ultrashort pulses. The interferenee eontribution is isolated by heterodyne deteetion. Note that the stnieture in the interferogram oeeurs only at multiples of 300 fs, the exeited-state vibrational period of f. it is only at these times that the wavepaeket promoted by the first pulse is baek in the Franek-Condon region. For a phase shift of 0 between the pulses the returning wavepaeket and the newly promoted wavepaeket are in phase, leading to eonstnietive interferenee (upper traee), while for a phase shift of n the two wavepaekets are out of phase, and interfere destnietively (lower traee). Reprinted from Seherer N F et 0/1991 J. Chem. Phys. 95 1487.

Figure Al.6.14. Schematic diagram showing the promotion of the initial wavepacket to the excited electronic state, followed by free evolution. Cross-correlation fiinctions with the excited vibrational states of the ground-state surface (shown in the inset) detennine the resonance Raman amplitude to those final states (adapted from [14].

Figure Bl.3.5. Four WMEL diagrams for fiilly resonant Raman scattering (RRS). Diagrams (a) and (b) both have doorway stage rr(A.j2 ) (Figure B 1.3.4(a)), in which a vibrational coherence is created in the ground electronic state, g. For the window event in (a), field 1 promotes the bra from the ground electronic state, g, to...

Related results of promotion (catalysis) and inliibition of stereonuitation by vibrational excitation have also been obtained for the much larger molecule, aniline-NHD (CgH NHD), which shows short-time chirality and stereonuitation [104. 105]. This kind of study opens the way to a new look at kinetics, which shows coherent and mode-selective dynamics, even in the absence of coherent external fields. The possibility of enforcing coherent dynamics by fields ( coherent control ) is discussed in chapter A3.13. 

These charge-transfer structures have been studied [4] in terms a very limited number of END trajectories to model vibrational induced electron tiansfer. An electronic 3-21G-1- basis for Li [53] and 3-21G for FI [54] was used. The equilibrium structure has the geometry with a long Li(2)—FI bond (3.45561 a.u.) and a short Li(l)—H bond (3.09017 a.u.). It was first established that only the Li—H bond stietching modes will promote election transfer, and then initial conditions were chosen such that the long bond was stretched and the short bond compressed by the same (%) amount. The small ensemble of six trajectories with 5.6, 10, 13, 15, 18, and 20% initial change in equilibrium bond lengths are sufficient to illustrate the approach. 

From the ground to an excited electronic state the electron promotion involved is likely to be to a less strongly bonding orbital, leading to an increase in molecular size and a decrease in rotational constants. The effect on the rotational fine structure is to degrade it to low wavenumber to give a strongly asymmetrical structure, unlike the symmetrical structure typical of vibrational transitions. 

The process steps listed in Table I9-I can sometimes be used to promote mixing. However, they are primarily for funcI ions other than solids mixing. (Note precautions for pneumatic conveying and vibrating in Table I9-I.)... 

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