Intramolecular vibrational energy spectroscopy

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... 

Boyarkin O V and Rizzo T R 1996 Secondary time scales of intramolecular vibrational energy redistribution in CFgH studied by vibrational overtone spectroscopy J. Chem. Phys. 105 6285-92... 

An alternative spectroscopic approach would be to determine the rotational temperature from the intensities in a rotationally resolved vibrational or electronic spectrum. In this case, even if one cannot resolve individual rovihrational transitions, one can still estimate the temperature by simulating the rotational contour of an individual vibronic band [120]. For this, one needs to know the rotational constants of the molecule and the direction of the transition moment however, even rough estimates of these quantities can lead to a reasonable temperature estimate. In measuring either Doppler widths or rotational band contours, the linewidth one obtains may contain a contribution from the finite lifetime of the molecule, determined by its intramolecular vibrational energy redistribution and/or dissociation rate if some type of photofragment spectroscopy is used, and this can make the temperature appear to be higher than it really is. 

Gatti F, lung C (2009) Intramolecular vibrational energy redistribution and infrared spectroscopy. In Meyer H-D, Gatti F, Worth GA (eds) Multidimensional quantum dynamics MCTDH theory and applications. WUey, Weinheim, pp 275—291... 

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. 

An intermediate epoxy ketene (39) from a-cleavage of 2,5-diphenyl-3(2H)-furanone (40) has been proposed by Padwa and co-workers to explain photoisomerization to 4,5-diphenyl-2(5H)-furanone (47)38. The epoxy ketene was not observed when the irradiation was monitored by infrared spectroscopy and was not trapped by methanol. The authors suggest that the intermediate may be formed with excess vibrational energy and as a result undergo very rapid intramolecular reaction. 

It has in fact been anticipated for many years that the CT free energy surfaces may deviate from parabolas. A part of this interest is provoked by experimental evidence from kinetics and spectroscopy. Eirst, the dependence of the activation free energy, Ff , for the forward (/ = 1 ) and backward i = 2) reactions on the equilibrium free energy gap AFq (ET energy gap law) is rarely a symmetric parabola as is suggested by the Marcus equation,Eq. [9]. Second, optical spectra are asymmetric in most cases and in some cases do not show the mirror symmetry between absorption and emission.In both types of experiments, however, the observed effect is an ill-defined mixture of the intramolecular vibrational excitations of the solute and thermal fluctuations of the solvent. The band shape analysis of optical lines does not currently allow an unambiguous separation of these two effects, and there is insufficient information about the solvent-induced free energy profiles of ET. 

The shape of the minimum in the surface is experimentally probed by vibrational spectroscopy. It is here that the computations can make direct coimection with experimental information. Formation of the H-bond from a pair of isolated molecules converts three translational and three rotational degrees of freedom of the formerly free pair of molecules into six new vibrations within the complex. The frequencies of these modes are indicative of the functional dependence of the energy upon the corresponding geometrical distortions. But rather than consisting of a simple motion, for example, H-bond stretch, the normal modes are composed of a mixture of symmetry-related atomic motions, complicating their analysis in terms of the simpler motions. In addition to these new intermoleeular modes, the intramolecular vibrations within each of the subunits are perturbed by the formation of the H-bond. The nature of each perturbation opens a window into the effects of the H-bond upon the molecules involved. The intensities of the various vibrations carry valuable information about the electron density within the complex and the perturbations induced by the formation of the H-bond. 

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