Response to “Comment on ‘Isotope effects in liquid water by infrared spectroscopy. IV. No free OH groups in liquid water’” [J. Chem. Phys. 135, 117101 (2011)

Abstract

The original infrared spectra in the OH stretch region that Riemenschneider and Ludwig (thereafter, RL) have obtained for pure water and aqueous salt solutions are very similar to what we have previously reported [J.-J. Max and C. Chapados, J. Chem. Phys. 115, 6803 (2001)]. In our 2010 paper, we claimed that “free” OH is not present in pure liquid water. The difference spectra from the salt solutions and pure water spectrum give small negative components situated near 3655 cm−1. Because this position is in the range where free OH groups should absorb RL assigned the negative peaks to free OH removed from pure water. That is, RL consider that pure liquid water contains free OH groups which are removed in the salt solutions. Obviously, the removal of all free OH present in pure water will produce maximum negative intensities in the difference spectra. In this response, we present unpublished difference spectra between several salt solutions and pure water where negative peaks are higher than that claimed by RL for pure water. Since this is impossible it demonstrates that the assignment proposed by RL to free OH is incorrect. The negative peaks come from the difference between large components that differ a little between salt solutions and pure water [J.-J. Max and C. Chapados, J. Chem. Phys. 115, 6803 (2001)]. Recall that the ionized salts do not absorb but perturb the surrounding water molecules.