Calculated proton affinities for some molecules containing group VIA atoms

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Abstract
The proton affinities and structures of a series of small molecules containing group VIA atoms are calculated via ab initio electronic structure techniques. The series under study included CX, OCX, XCX, and H2CX, where X=O, S, Se, and Te. In those cases where multiple protonation sites are available, a definitive assignment of the most stable site is reported. Excellent agreement with the experimentally known proton affinities is found in almost all cases. The results indicate that the general trend which one would expect upon moving down a column of the periodic table is born out, with a particularly large change on going from the first to the second row. Calculations were performed at both the SCF and correlated levels with compact effective potentials used to replace the core electrons. Complete structural optimizations via analytic gradients were performed utilizing basis sets of at least double zeta plus polarization quality.