TY - JOUR
T1 - Quantum mechanical tunnelling
T2 - The missing term to achieve sub-kJ mol-1barrier heights
AU - Kozuch, Sebastian
AU - Schleif, Tim
AU - Karton, Amir
N1 - Funding Information:
S. K. acknowledges the Israeli Science Foundation (grant no. 841/19). T. S. acknowledges the Deutsche Forschungs-gemeinschaft (DFG) under Germany’s Excellence Strategy – EXC 2033 – 390677874 – RESOLV; 331085229/GRK 2376. A. K. acknowledges an Australian Research Council Future Fellowship (Project No. FT170100373).
Publisher Copyright:
© 2021 the Owner Societies.
PY - 2021/5/14
Y1 - 2021/5/14
N2 - To predict barrier heights at low temperatures, it is not enough to employ highly accurate electronic structure methods. We discuss the influence of quantum tunnelling on the comparison of experimental and theoretical activation parameters (Ea, ΔH‡, ΔG‡, or ΔS‡), since the slope-based experimental techniques to obtain them completely neglect the tunnelling component. The intramolecular degenerate rearrangement of four fluxional molecules (bullvalene, barbaralane, semibullvalene, and norbornadienylidene) were considered, systems that cover the range between fast deep tunneling and small but significant shallow tunnelling correction. The barriers were computed with the composite W3lite-F12 method at the CCSDT(Q)/CBS level, and the tunnelling contribution with small curvature tunnelling. While at room temperature the effect is small (∼1 kJ mol-1), at low temperatures it can be considerable (in the order of tens of kJ mol-1 at ∼80 K).
AB - To predict barrier heights at low temperatures, it is not enough to employ highly accurate electronic structure methods. We discuss the influence of quantum tunnelling on the comparison of experimental and theoretical activation parameters (Ea, ΔH‡, ΔG‡, or ΔS‡), since the slope-based experimental techniques to obtain them completely neglect the tunnelling component. The intramolecular degenerate rearrangement of four fluxional molecules (bullvalene, barbaralane, semibullvalene, and norbornadienylidene) were considered, systems that cover the range between fast deep tunneling and small but significant shallow tunnelling correction. The barriers were computed with the composite W3lite-F12 method at the CCSDT(Q)/CBS level, and the tunnelling contribution with small curvature tunnelling. While at room temperature the effect is small (∼1 kJ mol-1), at low temperatures it can be considerable (in the order of tens of kJ mol-1 at ∼80 K).
UR - http://www.scopus.com/inward/record.url?scp=85106195856&partnerID=8YFLogxK
U2 - 10.1039/d1cp01275d
DO - 10.1039/d1cp01275d
M3 - Article
C2 - 33908522
AN - SCOPUS:85106195856
SN - 1463-9076
VL - 23
SP - 10888
EP - 10898
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
IS - 18
ER -