A Theoretical Study of Synchronous Proton Transfer in (HF)n, (H2O) n, and (HCl) n Where n = 3, 4, 5
Date of Award
Chemistry and Biochemistry
Gregory S. Tschumper
Ryan C. Fortenberry
Walter E. Cleland
For (HF)n, (H2O)n, and (HCl)n (n = 3 − 5), we have rigorously characterized the structures for the minima and transition states for synchronous proton transfer (SPT) with the CCSD(T) method and aug-cc-pVTZ basis set. The electronic barrier heights (∆E†) associated with these transition states have also been computed with the explicitly correlated CCSD(T)-F12 method and the aug-cc-pVQZ-F12 basis set (abbreviated aQZ-F12). (HCl)n (n = 3 − 5) SPT transition states have not been previously identified to the best of our knowledge, and they have been found to have D3h, D2d, and C1 point group symmetry, respectively. Our CCSD(T)-F12/aQZ-F12 computations for the hydrogen fluoride clusters indicate that the electronic barrier heights for SPT in the tetramer and pentamer are nearly identical at the CBS limit, and we observe the following trend for their electronic barriers: n = 4 ≈ n = 5 << n = 3 with ∆E† values of 14.77 kcal mol−1, 14.80 kcal mol−1, and 20.67 kcal mol−1, respectively. For water clusters, our results suggest that CCSD(T)-F12/aQZ-F12 barrier heights for (H2O)3 and (H2O)5 are quite similar near the CBS limit and that ∆E† is appreciably smaller for (H2O)4: (26.87 kcal mol−1 for n = 4 < 29.98 kcal mol−1 for n = 3 ≲ 30.40 kcal mol−1 for n = 5). In contrast to the HF and water clusters, our CCSD(T)-F12/aQZ-F12 electronic barrier heights for the hydrogen chloride clusters vary monotonically with the size of the cluster: n = 3 < n = 4 << n = 5 with ∆E† values of 27.38 kcal mol−1, 30.84 kcal mol−1, and 37.89 kcal mol−1, respectively. For all HF, H2O, and HCl clusters, our CCSD(T)-F12/aQZ-F12 barrier heights indicate that MP2 significantly underestimates ∆E† but reproduces the overall trends for the systems.
Yang, Johnny, "A Theoretical Study of Synchronous Proton Transfer in (HF)n, (H2O) n, and (HCl) n Where n = 3, 4, 5" (2021). Honors Theses. 1766.
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