Systematic analysis of electronic barrier heights and widths for concerted proton transfer in cyclic hydrogen bonded clusters: (HF) n , (HCl) n and (H 2 O) n where n = 3, 4, 5
The MP2 and CCSD(T) methods are paired with correlation consistent basis sets as large as aug-cc-pVQZ to optimize the structures of the cyclic minima for (HF) , (HCl) and (H O) where = 3-5, as well as the corresponding transition states (TSs) for concerted proton transfer (CPT). MP2 and CCSD(T) harm...
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Published in | Physical chemistry chemical physics : PCCP Vol. 26; no. 16; pp. 12483 - 12494 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
England
Royal Society of Chemistry
24.04.2024
|
Subjects | |
Online Access | Get full text |
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Summary: | The MP2 and CCSD(T) methods are paired with correlation consistent basis sets as large as aug-cc-pVQZ to optimize the structures of the cyclic minima for (HF)
, (HCl)
and (H
O)
where
= 3-5, as well as the corresponding transition states (TSs) for concerted proton transfer (CPT). MP2 and CCSD(T) harmonic vibrational frequencies confirm the nature of each minimum and TS. Both conventional and explicitly correlated CCSD(T) computations are employed to assess the electronic dissociation energies and barrier heights for CPT near the complete basis (CBS) limit for all 9 clusters. Results for (HF)
are consistent with prior studies identifying
and
point group symmetry for the minima and TSs, respectively. Our computations also confirm that CPT proceeds through
TS structures for the
minima of (H
O)
and (H
O)
, whereas the process goes through a TS with
symmetry for the
global minimum of (H
O)
. This work corroborates earlier findings that the minima for (HCl)
, (HCl)
and (HCl)
have
,
and
point group symmetry, respectively, and that the
structures are not minima for
= 4 and 5. Moreover, our computations show the TSs for CPT in (HCl)
, (HCl)
and (HCl)
have
,
, and
point group symmetry, respectively. At the CCSD(T) CBS limit, (HF)
and (HF)
have the smallest electronic barrier heights for CPT (≈15 kcal mol
for both), followed by the HF trimer (≈21 kcal mol
). The barriers are appreciably higher for the other clusters (around 27 kcal mol
for (H
O)
and (HCl)
; roughly 30 kcal mol
for (H
O)
, (H
O)
and (HCl)
; up to 38 kcal mol
for (HCl)
). At the CBS limit, MP2 significantly underestimates the CCSD(T) barrier heights (
, by
2, 4 and 7 kcal mol
for the pentamers of HF, H
O and HCl, respectively), whereas CCSD overestimates these barriers by roughly the same magnitude. Scaling the barrier heights and dissociation energies by the number of fragments in the cluster reveals strong linear relationships between the two quantities and with the magnitudes of the imaginary vibrational frequency for the TSs. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1463-9076 1463-9084 |
DOI: | 10.1039/d4cp00422a |