XXXVI Reunión Bienal de la Real Sociedad Española de Física

Acid dissociation in microsolvated environments

19 Jul 2017, 16:25

20m

Aula Matemáticas (Facultad de Química (USC))

Oral parallel contribution Molecular Physics at the Edge Molecular Physics at the Edge II

Description

The long-standing and fundamental question regarding the minimum number of water molecules required to dissociate an acid molecule in an aqueous microsolvation environment still remains open. For HCl interacting with water molecules - one added after the other - there is convincing evidence that an ion pair, and thus the dissociated acid molecule, can be stabilized using a minimum number of only four water molecules (see Fig. 1) [1,2]. However, this number has been questioned both on the experimental [3–6] and the theoretical sides [7]. In this respect, an experiment appeared recently in the literature [8] which suggested a new approach. In this experiment the dipole moment of HCl•(H2O)n clusters was measured as a function of the number of water molecules (see Fig. 2). The key result of those measurements was a noticeable rise of the total dipole moment of these clusters when n=6. A tempting explanation was to assign this sudden rise in the dipole moment to the dissociation of the HCl molecule. In this work, ab initio path integral calculations were performed in order to try to disentangle the controversy of whether it is 4 or 6 water molecules the minimum required to dissociate the chloridric acid. Our results show that measuring the dipole moment of HCl•(H2O)n clusters does not give any information about the dissociative state of the HCl molecule. In addition, a detailed analysis of thermal and quantum effects provides a much clearer picture of the acid dissociation process in microsolvated environments. The Cluster of Excellence “RESOLV” (EXC 1069) funded by the Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged along with computer time support from HPC-RESOLV, HPC@ZEMOS, BOVILAB@RUB and RV-NRW. References [1] A. Gutberlet, G. Schwaab, Ö. Birer, M. Masia, A. Kaczmarek, H. Forbert, M. Havenith, D. Marx, Science 324 (2009) 1545. [2] H. Forbert, M. Masia, A. Kaczmarek-Kedziera, N. N. Nair, D. Marx, J. Am. Chem. Soc. 133, (2011) 4062. [3] D. Skvortsov, S. J. Lee, M. Y. Choi, and A. F. Vilesov, J. Phys. Chem. A 113, (2009) 7360 . [4] S. D. Flynn, D. Skvortsov, A. M. Morrison, T. Liang, M. Y. Choi, G. E. Douberly, A. F. Vilesov, J. Phys. Chem. Lett. 1 (2010) 2233. [5] A. M. Morrison, S. D. Flynn, T. Liang, G. E. Douberly, J. Phys. Chem. A 114 (2010) 8090. [6] M. Letzner, S. Gruen, D. Habig, K. Hanke, T. Endres, P. Nieto, G. Schwaab, L. Walewski, M. Wollenhaupt, H. Forbert, D. Marx, M. Havenith, J. Chem. Phys. 139 (2013) 154304. [7] A. Vargas-Caamal, J. L. Cabellos, F. Ortiz-Chi, H. S. Rzepa, A. Restrepo, G. Merino, Chem. Eur. J. 22 (2016) 2812. [8] N. Guggemos, P. Slavíček, V. V. Kresin, Phys. Rev. Lett. 114 (2015) 043401.