We have used Raman spectroscopy to measure the most prominent and assignable vibrational frequencies of a number of ruthenium ammine and other transition metal complexes (as well as some small organics) in both H2O and D2O solutions.  The spectral data were compared to ab-initio calculations carried out at the B3LYP/6-311g+(2d,p)/SDD level using the polarized-continuum model of solvation (PCM) along with explicit waters of hydration in select cases.  The frequency �scaling factor� necessary to align calculated frequencies with experiment was determined over the spectral range of  3200-190 cm-1 (where the scale factor is defined by the ratio ?experiment/?calculated).  The aggregate set of frequency scaling factors so-determined exhibited a distinct and non-linear dependence on wavelength over this range (trending to higher values at lower frequencies).  This result suggests that in at least some cases the standard practice of applying a single scaling factor over the entire vibrational frequency range could introduce significant error, especially in the lower-frequency range where hydrogen-bonding effects and the importance of collective, anharmonic and medium-coupled modes can be important.  This refinement could also hold relevance to the calculated thermo-chemical properties of reactant species in solution and the related computational energy landscapes used for gaining insight into reactive processes.

Raman spectroscopic and ab-initio computational investigations demonstrate a significant wavelength-dependence in the vibrational frequency "scaling factor" needed to align theory at the B3LYP/6-311g+(2d,p)/ECP level with experiment for a selection of transition metal complexes and small organics in aqueous solution

248th National Meeting (2014)

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