posted on 2015-05-28, 00:00authored byChristopher 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.