Molecular
Distances Determined with Resonant Vibrational
Energy Transfers
- Publication date
- Publisher
Abstract
In general, intermolecular distances
in condensed phases at the
angstrom scale are difficult to measure. We were able to do so by
using the vibrational energy transfer method, an ultrafast vibrational
analogue of Förster resonance energy transfer. The distances
among SCN<sup>–</sup> anions in KSCN crystals and ion clusters
of KSCN aqueous solutions were determined with the method. In the
crystalline samples, the closest anion distance was determined to
be 3.9 ± 0.3 Å, consistent with the XRD result. In the 1.8
and 1 M KSCN aqueous solutions, the anion distances in the ion clusters
were determined to be 4.4 ± 0.4 Å. The clustered anion distances
in aqueous solutions are very similar to the closest anion distance
in the KSCN crystal but significantly shorter than the average anion
distance (0.94–1.17 nm) in the aqueous solutions if ion clustering
did not occur. The result suggests that ions in the strong electrolyte
aqueous solutions can form clusters inside of which they have direct
contact with each other