Predicting and characterizing new molecular species at a high-level theoretical approach: HSeCl, HClSe, and SeCl

New molecular species HSeCl, HClSe, and SeCl were investigated at a high level of theory, CCSD(T), with a series of correlation consistent basis sets with extrapolation to the CBS limit. Account has been taken for valence-only and core-valence correlation effects, and of anharmonic effects on the vibrational frequencies. HSeCl is 43.25 kcal mol−1 more stable than HClSe. A barrier (ΔG#) of 47.20 kcal mol−1 separates these species. Internuclear distances are generally overestimated by 0.008 Å in the valence-only correlation calculations. Inclusion of anharmonicity leads to much improved vibrational frequencies. For SeCl, we estimate ΔHf (0 K) = 23.96 and ΔHf (298.15 K) = 24.64 kcal mol−1; for HSeCl, we had 4.20 and 4.97 kcal mol−1, respectively.