Comparison of the Microsolvation of CaX (X = F, Cl, Br, I) in Water: Size-Selected Anion Photoelectron Spectroscopy and Theoretical Calculations.

J Phys Chem A

Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.

Published: April 2021

To understand the microsolvation of alkaline-earth dihalides in water and provide information about the dependence of solvation processes on different halides, we investigated CaBr(HO), CaI(HO), and CaF(HO) ( = 0-6) clusters using size-selected anion photoelectron spectroscopy and conducted theoretical calculations on these clusters and their neutrals. The results are compared with those of CaCl(HO) clusters reported previously. It is found that the vertical detachment energies (VDEs) of CaCl(HO), CaBr(HO), and CaI(HO) show a similar trend with increasing cluster size, while the VDEs of CaF(HO) show a different trend. The VDEs of CaF(HO) are much lower than those of CaCl(HO), CaBr(HO), and CaI(HO). A detailed probing of the structures shows that a significant increase of the Ca-X distance (separation of Ca-X ion pair) in CaCl(HO), CaBr(HO), and CaI(HO) clusters occurred at about = 5. However, for CaF(HO), no abrupt change of the Ca-F distance with the increasing cluster size has been observed. In CaCl(HO), CaBr(HO), and CaI(HO), the Ca atom coordinates directly with 5 HO molecules. However, in CaF(HO), the Ca atom coordinates directly with only 2 or 3 HO molecules. The similarity or differences in the structures and coordination numbers are consistent with the fact that CaCl, CaBr, and CaI have similar solubility, while CaF has much lower solubility.

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http://dx.doi.org/10.1021/acs.jpca.1c00573DOI Listing

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