Intermolecular proton binding in the presence of a large electric dipole: Ar-tagged vibrational predissociation spectroscopy of the CH3CN x H+ x OH2 and CH3CN x D+ x OD2 complexes.
We report Ar-predissociation vibrational spectra of the binary proton-bound hydrates of acetonitrile (AN), AN x H(+) x OH(2) and AN x D(+) x OD(2), in the 600-3800 cm(-1) energy range. This complex was specifically chosen to explore the nature of the intermolecular proton bond when there is a large difference between the electric dipole moments of the two tethered molecules. Sharp, isotope-dependent bands in the vicinity of 1000 cm(-1) are traced to AN x H(+) x OH(2) vibrations involving the parallel displacement of the shared proton along the heavy atom axis, nu(sp)(parallel). These transitions lie much lower in energy than anticipated by a recently reported empirical trend which found the nu(sp)(parallel) fundamentals to be strongly correlated with the difference in proton affinities (DeltaPA) between the two tethered molecules (Roscioli et al., Science, 2007, 316, 249). The different behavior of the AN x H(+) x OH(2) complex is discussed in the context of the recent theoretical prediction (Fridgen, J. Phys. Chem A., 2006, 110, 6122) that a large disparity in dipole moments would lead to such a deviation from the reported (DeltaPA) trend.
Gardenier
George H
GH
Sterling Chemistry Laboratory, Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, USA.
Roscioli
Joseph R
JR
Johnson
Mark A
MA