Face, Notch, or Edge? Intermolecular dissociation energies of 1-naphthol complexes with linear molecules

The stimulated-emission-pumping/resonant 2-photon ionization (SEP-R2PI) method was used to determine the intermolecular dissociation energies D₀ of jet-cooled 1-naphthol(1NpOH)·S complexes, where S is a linear molecule (N₂, CO, CO₂, OCS, N₂O, and ethyne) or symmetric-top molecule (2-butyne) that contains double or triple bonds. The dissociation energies D₀(S₀) are bracketed as follows: 6.68 ± 0.08 kJ/mol for S=N₂, 7.7 ± 0.8 kJ/mol for CO, 12.07 ± 0.10 kJ/mol for CO₂, 13.03 ± 0.01 kJ/mol for N₂O, 14.34 ± 0.08 kJ/mol for ethyne, 15.0 ± 1.35 kJ/mol for OCS, and 29.6 ± 2.4 kJ/mol for 2-butyne. The minimum-energy structures, vibrational wavenumbers, and zero-point vibrational energies were calculated using the dispersion-corrected density functional theory methods such as B97-D3 and B3LYP-D3 with the def2-QZVPP basis set. These predict that N₂ and CO are dispersively bound Face complexes (S bound to a naphthalene Face), while CO₂, N₂O, and OCS adsorb into the “Notch” between the naphthyl and OH groups; these are denoted as Notch complexes. Ethyne and 2-butyne form Edge complexes involving H-bonds from the —OH group of 1NpOH to the center of the molecule. The presence of a double or triple bond or an aromatic C=C bond within S does not lead to a specific calculated geometry (Face, Notch or Edge). However, a correlation exists between the structure and the sign of the quadrupole moment component Θ_zz of S: negative Θ_zz correlates with Face or Notch, while positive Θ_zz correlates with Edge geometries.