The SX diatomics, X = first- or second-row atom, have been studied employing coupled cluster theory and
the aug-cc-pV(X+d)Z basis sets. To estimate Δ
f
H°298, we have included a correction for core−valence (CV)
correlation, spin−orbit splitting, and scalar-relativistic (SR) effects. For SO and SC, the estimated Δ
f
H°298
values are 0.5 kcal/mol within the experiment. However, for the remaining molecules, a revision of their
ΔH°
f
,298 are required. Deviations as large as 10 kcal/mol have been found between our best estimates and the
values adopted by the NIST-JANAF tables. The proposed Δ
f
H°298 (±0.5kcal/mol) are 67.6 (SB), 66.7 (SN),
0.8 (SF), 47.4 (SAl), 27.9 (SSi), 38.1 (SP), 29.4 (S2), and 27.1 (SCl) kcal/mol. For comparative purposes we
performed BD(T), G3, CBS-QB3, B3LYP, and B3PW91 calculations. The mean absolute error (MAE) of the
G3 and CBS-QB3 Δ
f
H°298 with respect to our best results is 1.0 kcal/mol for both methodologies, whereas
for B3LYP/6-311+G(3df) and B3PW91/6-311+G(3df), the MAE is 1.6 and 2.0 kcal/mol, respectively. At
the coupled cluster level of theory, with respect to the experiment, the MAE of the equilibrium bond lengths
is 0.0013 and 0.0012 Å for the first- and second-row SX, respectively. This result involves extrapolation to
the CBS limit, a correction for CV and SR effects, and also a correction for complete triple excitations. Two
molecules presented an unstable HF wave function, SN and SP. In both cases, the use of the CCSDT and
BD(T) methods outperformed CCSD(T). Our spin−orbit corrected coupled cluster adiabatic electron affinities
(EAad) are ±0.7 kcal/mol within the experiment for SN, SO, SF, and S2. However, some discrepancies were
found for SC and SAl. Our best estimates are EAad(SC) = 2.3 kcal/mol and EAad(SAl) = 62.5 kcal/mol, 2.4
and 1.6 kcal/mol larger than the experimental EAad, respectively. For SB, SSi, SP, and SCl, we propose new
EAad of 53.7, 12.4, 36.5, and 59.0 kcal/mol, respectively. The MAE of the CBS-QB3 and G3 EAad with
respect to our estimated EAad is 0.9 kcal/mol for both methodologies, whereas for B3LYP/6-311+G(3df) and
B3PW91/6-311+G(3df), the MAE are 1.9 and 2.7 kcal/mol, respectively, but 50% of the error is provided
only by SC and SN.