Direct Test of the Equivalency of Dynamic IR and Dynamic Raman Spectroscopies As Techniques for Observing Ultrafast Molecular Dynamics

Abstract

We report the temperature-dependent infrared (IR) and Raman spectra of Fe(CO)3(η(4)-norbornadiene). This molecule undergoes carbonyl ligand site exchange on the vibrational time scale, and the effect of this exchange is observable as coalescence of the carbonyl bands in both the IR and Raman spectra. We outline a theory that we used to account for these effects and report simulations of the experimental spectra. We used these simulations to extract the carbonyl ligand exchange rates at various temperatures from the IR and Raman data. This data was used to calculate the activation energy for carbonyl exchange, yielding activation energies of 1.2 ± 0.2 and 1.4 ± 0.1 kcal/mol from the IR and Raman data, respectively. These activation energies are statistically identical and are consistent with previously reported values. This constitutes the first direct comparison between dynamic IR and Raman spectroscopies, and we find them to give identical results.

Infrared Dynamics of Iron Carbonyl Diene Complexes

“…Most notably, in a series of impressive papers, Lear and colleagues have examined some subtle effects on the chemical exchange in the diene complexes. They have shown that Raman spectroscopy mimics the IR data, giving activation energies for NBD in 2-methylpentane of 1.2 ± 0.2 and 1.4 ± 0.1 kcal/mol from IR and Raman data, respectively. The rate constants varied from 1.15 × 10 12 s –1 at 293 K to 0.48 × 10 12 s –1 at 213 K. In other words they get essentially identical results to Grevels 1 .…”

Ionicity of Protic Ionic Liquid: Quantitative Measurement by Spectroscopic Methods

“…Compared with NMR, the IR spectrum has a much shorter time scale of 10 −13 s, enough to reflect information on different functional groups by presenting peaks of different shift areas on the spectrum. 18 Areas of characteristic peaks on the IR spectrogram can reflect the relative amount of corresponding substances. However, the ionicity could be determined accurately in case the standard curve was established between the peak area and quantity of substances.…”

Structure and Dynamics of Iron Pentacarbonyl

“…In several elegant experiments, Lear and co-workers 32−34 extended these experiments and essentially confirmed Grevels's conclusions. It is worth mentioning that two authors 30,32 have suggested a mistake in McClung's method, but a careful analysis of the mathematics shows that the supposed error is due only to an unconventional definition and that in fact McClung's method is essentially the same as theirs.…”