## Abstract

The interaction between HCl and H_{2}O is of considerable theoretical and experimental interest due to its important role in atmospheric chemistry and understanding the onset of the dissociation of HCl in water. In this work, the HCl-H_{2}O complex is quantitatively characterized in two ways. First, we report a new full-dimensional potential energy surface (PES) for the HCl + H_{2}O system. The nine-dimensional (9D) PES is based oncirca43 000ab initiopoints calculated at the level of CCSD(T)-F12a/AVTZ with the basis set superposition error correction using the permutation invariant polynomial-neural network method, which can accurately and efficiently reproduce the geometries, energies, frequencies of the complex of HCl with H_{2}O, as well as the relevant minimum energy path. Next, we present the results of the first fully coupled 9D quantum calculations of the intra- and intermolecular vibrational states of the HCl-H_{2}O dimer, performed on the new PES. They employ the highly efficient bound-state methodology previously used to compute accurately the rovibrational level structure of the H_{2}O/D_{2}O-CO and HDO-CO complexes [P. M. Felker and Z. Bačić,J. Chem. Phys., 2020,153, 074107;J. Phys. Chem. A, 2021,125, 980]. The 9D calculations characterize the vibrationally averaged nonplanar ground-state geometry of the HCl-H_{2}O complex, the intramolecular vibrational fundamentals of both H_{2}O and HCl moieties, and their frequency shifts, as well as the low-energy intermolecular vibrational states in each of the intramolecular vibrational manifolds and the effects of the coupling between the two sets of modes. The calculated properties of the HCl-H_{2}O dimer are in excellent agreement with the available spectroscopic data. The 9D computed dimer binding energyD_{0}of 1334.63 cm^{−1}agrees extremely well with the experimentalD_{0}equal to 1334 ± 10 cm^{−1}[B. E. Casterline and A. K. Mollner and L. C. Ch'ng and H. Reisler,J. Chem. Phys., 2010,114, 9774]. Moreover, the ground-state expectation value of the out-of-plane bend angle of H_{2}O, 33.80°, and the computed HCl stretch frequency shift, −157.9 cm^{−1}, both from the 9D calculations, are in very good accord with the corresponding experimental values.

Original language | English (US) |
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Pages (from-to) | 7101-7114 |

Number of pages | 14 |

Journal | Physical Chemistry Chemical Physics |

Volume | 23 |

Issue number | 12 |

DOIs | |

State | Published - Mar 28 2021 |

## ASJC Scopus subject areas

- Physics and Astronomy(all)
- Physical and Theoretical Chemistry