Internal electric fields in small water clusters [(H2O)n; n = 2–6]

Abstract

The electric field experienced by a water molecule within a water cluster depends on its position relative to the rest of the water molecules. The stabilization energies and the red-shifts in the donor O–H stretching vibrations in the water clusters increase with the cluster size concomitant with the increase in the electric field experienced by the donor O–H of a particular water molecule due to the hydrogen bonding network. The red-shifts in O–H stretching frequencies show a spread of about ±100 cm⁻¹ against the corresponding electric fields. Deviations from linearity were marked in the region of 100–160 MV cm⁻¹, which can be attributed to the strain in the hydrogen bonding network, especially for structures with DDAA and DDA motifs. The linear Stark effect holds up to 200 MV cm⁻¹ of internal electric field for the average red-shifts in the O–H stretching frequencies, with a Stark tuning rate of 2.4 cm⁻¹ (MV cm⁻¹)⁻¹, suggesting the validity of the classical model in small water clusters.