Intramolecular vibrational energy dimers

Another important question deals with the intramolecular and unimolecular dynamics of the X-—RY and XR -Y- complexes. The interaction between the ion and molecule in these complexes is weak, similar to the intermolecular interactions for van der Waals molecules with hydrogen-bonding interactions like the hydrogen fluoride and water dimers.16 There are only small changes in the structure and vibrational frequencies of the RY and RX molecules when they form the ion-dipole complexes. In the complex, the vibrational frequencies of the intramolecular modes of the molecule are much higher than are the vibrational frequencies of the intermolecular modes, which are formed when the ion and molecule associate. This is illustrated in Table 1, where the vibrational frequencies for CH3C1 and the Cr-CHjCl complex are compared. Because of the disparity between the frequencies for the intermolecular and intramolecular modes, intramolecular vibrational energy redistribution (IVR) between these two types of modes may be slow in the ion-dipole complex.16... 

The fragment excited-state NO(A2S+) is a molecular 3r Rydberg state, and we shall refer to this as NO(A, 3s). The observed NO(A, 3.v) product state distributions supported the notion of a planar dissociation involving restricted intramolecular vibrational energy redistribution (IVR) [176]. A scheme for studying NO dimer photodissociation dynamics via TRPES is depicted in Fig. 25. The NO(A, 3.v) + NO(X) product elimination channel, its scalar and vector properties, and its evolution on the femtosecond time scale have been discussed in a number of recent publications (see Ref. [175] and references cited therein). 

Pump-probe experiment is an efficient approach to detect the ultrafast processes of molecules, clusters, and dense media. The dynamics of population and coherence of the system can be theoretically described using density matrix method. In this chapter, for ultrafast processes, we choose to investigate the effect of conical intersection (Cl) on internal conversion (IC) and the theory and numerical calculations of intramolecular vibrational relaxation (IVR). Since the 1970s, the theories of vibrational relaxation have been widely studied [1-7], Until recently, the quantum chemical calculations of anharmonic coefficients of potential-energy surfaces (PESs) have become available [8-10]. In this chapter, we shall use the water dimer (H20)2 and aniline as examples to demonstrate how to apply the adiabatic approximation to calculate the rates of vibrational relaxation. 

Let us now introduce the electron-vibration interaction in the symmetric dimer, to account for the modulation of the site energies, and of the electron transfer integral, by the intramolecular vibrational modes and by the rigid molecular motions respectively. This leads us to the so-called Peierls—Hubbard model. ... 

Owing to their relatively simple electronic structure, the alkali trimers can be regarded as such model systems, to study, for example the principles of intramolecular vibrational redistribution (IVR) in photoexcited molecules or clusters. Among the alkali trimers Naa, especially when excited to its electronic B state, seems to be the best known. It acts in this section as a prototype for exploration of details of photoinduced IVR processes in real-time. Figure 3.35 sketches the principle of the experimental approach for triatomic s systems such as the Jahn-Teller distorted Naa B system. Compared to the investigations on the dimer systems, the only difference is that the energy surfaces involved get a dittle more complicated. 

As discussed in section A3.12.2. intrinsic non-RRKM behaviour occurs when there is at least one bottleneck for transitions between the reactant molecule s vibrational states, so drat IVR is slow and a microcanonical ensemble over the reactant s phase space is not maintained during the unimolecular reaction. The above discussion of mode-specific decomposition illustrates that there are unimolecular reactions which are intrinsically non-RRKM. Many van der Waals molecules behave in this maimer [4,82]. For example, in an initial microcanonical ensemble for the ( 211 )2 van der Waals molecule both the C2H4—C2H4 intennolecular modes and C2H4 intramolecular modes are excited with equal probabilities. However, this microcanonical ensemble is not maintained as the dimer dissociates. States with energy in the intermolecular modes react more rapidly than do those with the C2H4 intramolecular modes excited [85]. 

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