Vibrational activation

Symmetry mode Symmetry element E>egree of freedom Molecule Number of C—H M braiions Number of skeleton vibrations Activity of vibrations ... 

Container A is filled with 1.0 mol of the atoms of an ideal monatomic gas. Container B has 1.0 mol of atoms bound together as diatomic molecules that are not vibrationally active. Container C has 1.0 mol of atoms bound together as diatomic... 

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... 

Altoe P, Bemardi F, Garavelli M, Orlandi G, Negri F (2005) Solvent effects on the vibrational activity and photodynamics of the green fluorescent protein chromophore a quantum-chemical study. J Am Chem Soc 127 3952-3963... 

The pressure dependence of the reaction between butane-1-thiol and hydrogen atoms at 133, 266, 532, 2660, and 5320 Pa, using two types of fast-flow discharge reactors, have been studied. Butane and but-l-ene were the main products. Pressure dependence indicated decomposition through vibrationally activated species. 

This experimental work on the dissociation of excited Nal clearly demonstrated behavior one could describe with the vocabulary and concepts of classical motions.The incoherent ensemble of molecules just before photoexcitation with a femtosecond laser pump pulse was transformed through the excitation into a coherent superposition of states, a wave packet that evolved as though it represented a single vibrationally activated molecule. 

One issue that is particularly interesting for activated dissociation is the importance of translational vs. vibrational activation since this relates to the topology of the barrier location on the PES (see Section 2.3.1). In analyzing experiments, it has been traditional to define the vibrational efficacy rjv as in eq. (2.5). This analysis, however, assumes that A(v) is the same for all v and this may not be universally true. In this case, describing vibrational efficacy is more complicated. Very recently, experiments for CH4 dissociation on transition metals even combine supersonic nozzle molecular beams with laser state preparation techniques to probe the reactivity of specifically prepared vibration rotation states [115-118] (see Section 4.3.1.3). 

Figure 3.29 (a) shows measurements of S(E, 0i = 0, Tv, Ts), again emphasizing the importance of both translation and vibration in activating dissociation [267,268]. Of course, there are now many different modes of vibration for CH4 that are thermally excited and can contribute to the vibrational activation. Quantum chemistry [269] and DFT calculations [270] of the transition state and reduced dimensional dynamic models of the dissociation [59] suggest that the dominant vibrational effect is due to a single local —H stretch mode that points towards the surface. Fitting S(E, =... 

P. George and J. Griffith, in Enzymes, P. D. Boyer, H. Lardy and K. Myrback, eds., Vol. 1, p. 347, Academic Press, New York (1959). The first quantitative formulation of vibrational activation for redox reactions from first-layer ligands. 

R. A. Marcus, J. Chem. Phys. 93 679 (1965). The addition of the George and Griffith theory (vibrational activation) to electrostatics of electron transfer. 

C4H6 10 atoms, non-linear three translations, three rotations and 24 vibrations C3H4O eight atoms, non-linear three translations, three rotations and 18 vibrations activated complex 18 atoms three translations, three rotations, one internal translation and 47 vibrations... 

Consider first the one dimensional, classical problem of a diatomic molecule BC colliding with an atom A (Figure 3.1) to yield either vibrational activation or deactivation of BC. Suppose that the molecule is a harmonic oscillator with frequency v. If the interaction potential is... 

Fig. 5. Energy level diagram for Pd(2-thpy)2 dissolved in n-octane. The Tj state at 18,418 cm is zero-field split on the order of 0.2 cm. The emission decay times refer to the individual triplet suhstates I, II, and III, respectively, at T = 1.3 K. (Compare Fig. 6.) These suhstates are radiatively deactivated as purely electronic transitions, as well as by Franck-Condon (FC) and Herzberg-Teller (HT) vibrational activity, respectively. This leads the different vibrational satellites. (Compare also Sects. 4.2.2 and 4.2.3.) The lifetime of the S, state is determined from the homogeneous linewidth of the spectrally resolved Sq —> S, electronic origin. (Sect. 3.2) The electronic state at 24.7 x 10 cm is not yet assigned...

The vibrational satellite structures that occur in the emission and excitation spectra (e.g.see Figs. 13 to 15) result from different vibrational activities, namely from vibronic or Herzberg-Teller activity, as introduced in this section, and from Franck-Condon activity, as discussed in the next section. 

In a situation, when the purely electronic transition between an excited state and the ground state is allowed or not totally forbidden, a different vibrational activity, the Franck-Condon activity, can become dominant. This can lead, for example, to the occurrence of progressions. Although, the Franck-Condon effect is well known, it is appropriate to summarize briefly the background and to introduce the useful Huang-Rhys parameter. This summary is largely based on the descriptions found in the Refs. [96-100,154], in particular it is referred to Ref. [99, p. 200]. 

The 20 K emission spectrum shown in Fig. 14 exhibits vibrational satellites due to activity of fundamentals (e.g. 190, 383, 458, 718, 1400,1484 cm", etc.), of combinations of these fundamentals (e.g. (190 -l- 1484), (383 -l- 1400), (458 -l-1484), (718 + 1400), (718 -I- 1484) cm", etc.), and for the most intense satellites, one observes also the second members of progressions (e.g. 1 x 718 cm, 2 X 718 cm 1 X 1484 cm, 2 X 1484 cm ). These results can be rationalized well, when all vibrational satellites with significant intensity are assigned to correspond to totally symmetric fundamentals. This assignment is also in accordance with the observation that the same fundamentals are built upon the false origins occurring in the 1.3 K emission spectrum. (Fig. 13) An assignment to an alternative symmetry would not allow us to explain the very distinct differences of vibrational activities found in the emission of the states I and II, respectively. 

Similarly to CDMA and II, and in contrast to CTMA, the LIF excitation spectra for the other molecules considered (i.e., ABN [86, 92b], EIN [92b], 4-dialkylamino derivatives of pyrimidine (except VIII) [90] and benzoic acid esters, XI and XII [88, 91, 94]) show the characteristic pattern of low-frequency vibrations (Table 1). Similar patterns have been analyzed for alkylbenzenes and toluenes [111], fluorotoluene [112, 113a,b], m-cresol [113c], toluidines [113d] and dialkylanilines [87a, 114] in terms of the internal rotation of the methyl groups, torsion of the dialkylamino group and inversion. The precise nature of the vibrations active in the LIF spectra of the considered compounds is not yet clear, but it is most probably associated with torsion and inversion of the dialkylamino group [86, 87, 88b, 90c]. The lowest... 

Here 4 and p are the vectors of dimensionless coordinates and impulses, respectively, o>.is the frequency of the harmonic vibrations active in the Jahn-Teller effect a is the vibronic constant related to the usual F (Ber-... 

Adsorption on the interior surface of the tubes can take place. At high temperatures, hydrogen gas condenses to a liquid deep within the tubes, squeezing between the carbon nanotube plates and thus decreasing their vibration activity this allows for greater compression [1], To get the hydrogen into the fuel cell, a vacuum is pulled and the tube heated to 900°C. When hydrogen is inserted into the tube, a pressure of 12,000 kPa is used [1], A pressure of 4,000 kPa must be maintained to keep the H2 in place in the cell [1],... 

Analysis of the vibrational bands revealed that at earliest growth stages the film is amorphous. In particular, a broad band at 1373 cm-1 proves the amorphous nature of the film. On the other hand, the mode at 1606 cm-1, usually an infrared active band, proves a symmetry breakdown of the molecule at this growth stage. Additionally, the amorphous phase lacks of vibrational activity at the phenyl groups, and tetracene backbone. Therefore, it is likely that the geometry of the rubrene molecule is dramatically distorted. 

The up-pumping model says that instead of the molecule s vibrations becoming activated right at the shock front, there is a brief delay before vibrational activation occurs. This might be a trivial and unimportant feature of shock excitation—just an irrelevant brief delay-unless the nonequilibrium conditions that persist during this brief time play a significant role in shock initiation. Several possible ways that up-pumping can affect explosive sensitivity are discussed in the next section. 

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