Intramolecular vibrational redistribution dynamics

Beil A, Luckhaus D, Quack M and Stohner J 1997 Intramolecular vibrational redistribution and unimolecular reactions concepts and new results on the femtosecond dynamics and statistics in CHBrCIF Ber. Bunsenges. Phys. Chem. 101 311-28... 

In order to define how the nuclei move as a reaction progresses from reactants to transition structure to products, one must choose a definition of how a reaction occurs. There are two such definitions in common use. One definition is the minimum energy path (MEP), which defines a reaction coordinate in which the absolute minimum amount of energy is necessary to reach each point on the coordinate. A second definition is a dynamical description of how molecules undergo intramolecular vibrational redistribution until the vibrational motion occurs in a direction that leads to a reaction. The MEP definition is an intuitive description of the reaction steps. The dynamical description more closely describes the true behavior molecules as seen with femtosecond spectroscopy. 

Both Ok and fl. - flj. provide useful insights into the causes and rates of specific dynamical processes. Sections 9.4.9 and 9.4.10 provide analyses of the dynamics of the S-uncoupling operator in a 25+1A state and the 1 2 anharmonic coupling operator that contributes to Intramolecular Vibrational Redistribution (IVR) in a polyatomic molecule and illustrate the diagnostic power of the flk + fij. and lk — resonance and rate operators. 

When a bright basis-state is embedded in a dense manifold (quasi-continuum) of dark basis-states, a variety of dynamical processes ensue (Bixon and Jortner, 1968 Rhodes, 1983). These include Intramolecular Vibrational Redistribution (IVR), Inter-System Crossing (ISC), and Internal Conversion (IC). At t = 0, the bright basis state, which is not an eigenstate of H, is prepared, k(O) = bright ... 

Kab G, Schroder C, Schwarzer D (2002) Intramolecular vibrational redistribution and energy relaxation in solution a molecular dynamics approach. PCCP 4 271... 

The presentation by E.R. Bernstein of his work on the vibrational dynamics of aniline-Ar and aniline-CH4 van der Waals complexes has raised two major questions. The first one deals with the actual singificance of the more and more common and widely used expressions intramolecular vibrational redistribution (IVR) and vibrational predissociation (VP). These terms normally designates well-defined and often competing mechanisms ... 

As already discussed, the approximate QD signal of a 120fs pulse exhibits two dominant vibrations which are caused by the Qs mode (310 to 320 fs) on the one hand, and by a slow pseudorot at ional mode (1 ps) on the other hand. Interestingly, the vibration along the Qs mode loses its pronounced character after 3ps (see Fig.3.51), i.e. the wave packet spreads out along this coordinate, as a movie of the three-dimensional wave packet dynamics of the B state shows [388]. This observation has already been interpreted as an effect of the anharmonicity of the PES and as intramolecular vibrational redistribution from dominantly Qs to g and (f vibration [62, 81]. The behavior described is also reflected by the approximate QD pump probe signal where the oscillation of period 310 to 320 fs caused by the Qs mode vanishes after a time of 4 to 5ps (see also Fig. 3.52). 

J. Giraud-Girard, J. Manz, and Ch. Scheurer, Twist Dynamics of 9-(N-Carbazolyl)-Anthracene Effects of Intramolecular Vibrational Redistribution and Non-Adiabatic Transitions in Coupled Bright and Dark States , Z. Phys. D 39, 291 (1997). 

Wave packet propagation phenomena influenced by electronic perturbations and by intramolecular vibrational redistributions (IVR) these phenomena are studied for extremely cold alkali dimers (K2, Na2) and trimers (K3, Naa). A highlight is the possibility to control actively the molecular dynamics of these species under certain experimental conditions, by means of ultrashort laser pulses. 

This is no longer the case when (iii) motion along the reaction patir occurs on a time scale comparable to other relaxation times of the solute or the solvent, i.e. the system is partially non-relaxed. In this situation dynamic effects have to be taken into account explicitly, such as solvent-assisted intramolecular vibrational energy redistribution (IVR) in the solute, solvent-induced electronic surface hopping, dephasing, solute-solvent energy transfer, dynamic caging, rotational relaxation, or solvent dielectric and momentum relaxation. 

Callegari A, Rebstein J, Muenter J S, Jost R and Rizzo T R 1999 The spectroscopy and intramolecular vibrational energy redistribution dynamics of HOCI in the u(OH) = 6 region, probed by infrared-visible double resonance overtone excitation J. Chem. Phys. 111 123-33... 

Quasiclassical trajectory calculations are the method of choice for determining the dynamics of intramolecular vibrational energy redistribution leading to a chemical reaction. If this information is desired, an accurate reaction rate can be obtained at little extra expense. 

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... 

Reaction dynamics as opposed to reaction kinetics strives to unravel the fundamentals of reactions—just how they transpire, how intramolecular vibrational energy redistributions provide energy to the modes most involved along the reaction coordinate, how specihc reaction states progress to specihc product states, why product energy distributions and ratios of alternative products are as they are, and, of course, how fast the basic processes on an atomic scale and relevant timeframe occur. 

Reaction dynamics on the femtosecond time scale are now studied in all phases of matter, including physical, chemical, and biological systems (see Fig. 1). Perhaps the most important concepts to have emerged from studies over the past 20 years are the five we summarize in Fig. 2. These concepts are fundamental to the elementary processes of chemistry—bond breaking and bond making—and are central to the nature of the dynamics of the chemical bond, specifically intramolecular vibrational-energy redistribution, reaction rates, and transition states. 

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