American Chemical Society
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Accurate Calculation of the Dissociation Energy of the Highly Anharmonic System ClHCl

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journal contribution
posted on 2015-05-28, 00:00 authored by Christopher Stein, Rainer Oswald, Peter Botschwina, Kirk A. Peterson
Accurate bond dissociation energies (D0) are reported for different isotopologues of the highly anharmonic system ClHCl. The mass-independent equilibrium dissociation energy De was obtained by a composite method with frozen-core (fc) CCSD­(T) as the basic contribution. Basis sets as large as aug-cc-pV8­(+d)­Z were employed, and extrapolation to the complete basis set (CBS) limit was carried out. Explicitly correlated calculations with the CCSD­(T)-F12b method were also performed to support the conventionally calculated values. Core–core and core–valence correlation, scalar relativity, and higher-order correlation were considered as well. Two mass-dependent contributions, namely, the diagonal Born–Oppenheimer correction and the difference in zero-point energies between the complex and the HCl fragment, were then added in order to arrive at precise D0 values. Results for 35ClH35Cl and 35ClD35Cl are 23.81 and 23.63 kcal/mol, respectively, with estimated uncertainties of 0.05 kcal/mol. In contrast to FHF (Stein, C.; Oswald, R.; Sebald, P.; Botschwina, P.; Stoll, H., Peterson, K. A. Mol. Phys. 2013, 111, 2647−2652), the D0 values of the bichloride species are larger than their De counterparts, which is an unusual situation in hydrogen-bonded systems.