Vibrational energy flow transfer

Figure C3.5.11. IR-Raman measurements of vibrational energy flow tlirough acetonitrile in a neat liquid at 300 K, adapted from [41], An ultrashort mid-IR pulse pumps the C-H stretch, which decays in 3 ps. Only 1% of the energy is transferred to the C N stretch, which has an 80 ps lifetime. Most of the energy is transferred to the C-H bend plus about four quanta of C-C=N bend. The daughter C-H bend vibration relaxes by exciting the C-C stretch. The build-up of energy in the C-C=N bend mirrors the build-up of energy in the bath, which continues for about 250 ps after C-H stretch pumping.

The transfer and storage of vibrational energy in large and small molecules mediate a variety of molecular processes. A central motivation for the study of vibrational energy flow in molecules has long been its influence on chemical reaction kinetics in gas and condensed phases [1-11], as well as its role in... 

Another vibrational energy flow pathway is due to the vibrational energy transfer through the dipole-dipole interaction ... 

Hamilton C E, Bierbaum V M and Leone S R 1985 Product vibrational state distributions of thermal energy charge transfer reactions determined by laser-induced fluorescence in a flowing afterglow Ar" + CC -> CC (v= 0-6) + Ar J. Chem. Rhys. 83 2284-92... 

The first classical trajectory study of iinimoleciilar decomposition and intramolecular motion for realistic anhannonic molecular Hamiltonians was perfonned by Bunker [12,13], Both intrinsic RRKM and non-RRKM dynamics was observed in these studies. Since this pioneering work, there have been numerous additional studies [9,k7,30,M,M, ai d from which two distinct types of intramolecular motion, chaotic and quasiperiodic [14], have been identified. Both are depicted in figure A3,12,7. Chaotic vibrational motion is not regular as predicted by tire nonnal-mode model and, instead, there is energy transfer between the modes. If all the modes of the molecule participate in the chaotic motion and energy flow is sufficiently rapid, an initial microcanonical ensemble is maintained as the molecule dissociates and RRKM behaviour is observed [9], For non-random excitation initial apparent non-RRKM behaviour is observed, but at longer times a microcanonical ensemble of states is fonned and the probability of decomposition becomes that of RRKM theory. 

Conduction. In a solid, the flow of heat by conduction is the result of the transfer of vibrational energy from one molecule to another, and in fluids it occurs in addition as a result of the transfer of kinetic energy. Heat transfer by conduction may also arise from the movement of free electrons, a process which is particularly important with metals and accounts for their high thermal conductivities. 

This elastic energy will be transformed into thermal energy, that is, we observe the stimulation of thermal vibrations. All flowing processes therefore constitute a transfer of elastic (or dielectric) energy into thermal energy. As we see in Fig. 13 between the direction of an external stress o and that of the possible motion of a flowing unit we have an angle distance between the minimum and the saddle point will be r0. The distance related to the direction of the stress o is r0 cos tp. Therefore we external force from B to B will be F = o cos ip. 

Coulomb Force and Intramolecular Energy Flow Effects for Vibrational Energy Transfer for Small Molecules in Polar Solvents... 

This derivation is largely meant to be a schematic way of helping us see how the vibrational friction influences the rate of solute-solvent energy transfer. Notice, however, that we never specified the actual initial conditions of an experiment (in particular whether the solute was to be initially hot or cold with respect to the surrounding solvent). Without such a specification we cannot predict the net sign of the energy flow. 

The above considerations indicate that at some intermediate value of r, the I2 system on its way to form the completely equilibrated ground state will experience a significant charge flow, as charge localized l2 converts to charge-delocalized I2. Associated with this shift is a corresponding force that potentially can be quite effective in the transfer of vibrational energy. 

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