Determining Equilibrium Fluctuations Using Temperature-Dependent 2D-IR

Abstract

The structures of ground and transition states of each iron diene complex were calculated using density functional theory, as described in the text. Anharmonic frequency calculations were also performed on the ground state structures, to confirm that this was not a source of cross peak intensity. The Cartesian coordinates of each structure follow:

Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene

“…250 8C), the RCM using unmodified calculated n(CO) band wavenumbers ande xperimental value of DE reproduce the main features of the temperature dependence of the vibrational spectra of Fe(NBD)(CO) 3 ( Figure 6). [19] Conclusion Detailed consideration of the temperature dependence of the Q 7 and Q 8,9 modes of Fc demonstrate clearly that the calculated vibrational spectra of dynamic molecules must take into account the ground and transition states and the energy difference between these forms.S imple approximationso ft he impact of displacementsa longt he reactionc oordinate allow implementation of the RCM and are shownt op redict the temperatured ependence of the spectra in remarkably close qualitative agreement with experiment. In contrast to NMR-like lifetime broadening, the RCM can be related directly to transition state theory in am anner consistentw ith conclusions drawn from 2D-IR measurements of ultrafast relaxation of Fe(cyclooctadiene)(-CO) 3 .…”

“…In contrast to NMR-like lifetime broadening, the RCM can be related directly to transition state theory in am anner consistentw ith conclusions drawn from 2D-IR measurements of ultrafast relaxation of Fe(cyclooctadiene)(-CO) 3 . [19] Conclusion Detailed consideration of the temperature dependence of the Q 7 and Q 8,9 modes of Fc demonstrate clearly that the calculated vibrational spectra of dynamic molecules must take into account the ground and transition states and the energy difference between these forms.S imple approximationso ft he impact of displacementsa longt he reactionc oordinate allow implementation of the RCM and are shownt op redict the temperatured ependence of the spectra in remarkably close qualitative agreement with experiment. The temperature-dependent spectrao fg as, solution,f rozen solution,a nd crystalline solid forms of Fc can be explained within as elf-consistent framework using the RCM.…”

“…[19] Any description of dynamic effects in the vibrational spectra must take into account the spectra of the molecule in its ground and transition states andt he barrier for the dynamic process. Moreover,t he interpretative framework of the RCM sits comfortablyw ith ultrafast intramolecular vibrational redistributionm easured by 2D IR spectroscopy.…”

“…[17] The temperature dependence of the spectra has been modeled within af ormalism based on NMR-like rapid exchange between the normal modes, where there is ad ifferent rate of exchange between the three carbonyl normalm odes yielding estimates for the respectiver ate constants. [18] While the physical interpretation of the calculations is called into question by recent 2D-IR studies of relatedc omplexes, [19] the approach provides am eanso f investigatings olvation effects on the molecular dynamics [18] and the measurement of the rates of electron-transfer processes. [20] The barrier for the turnstile CO rotationo fF e(NBD)(CO) 3 is estimated to be ca.…”

“…Moreover,t he interpretative framework of the RCM sits comfortablyw ith ultrafast intramolecular vibrational redistributionm easured by 2D IR spectroscopy. [19] Any description of dynamic effects in the vibrational spectra must take into account the spectra of the molecule in its ground and transition states andt he barrier for the dynamic process. RCM can provide the interpretative framework for testinga nd refinement of ab initio methodsf or the calculation of ground and transition-state geometry and, importantly,establishing experimental methods forcharting the reactionc oordinate.…”