Spectroscopic Determination of Sequential Desorption Energies from Aromatic Surfaces

We have presented a mass-selective electronic spectroscopy approach to experimentally determine the sequential desorption energies of rare gas atoms from noncovalently bound complexes in the gas phase. Using the resonant two-photon ionization (R2PI) spectroscopy, the disappearance of Franck-Condon active vibrational bands was probed to indicate the desorption threshold in the excited state directly. The single Ar atom desorption energies from Np-Ar, Np-Ar₂, and Np-Ar₃ complexes were measured as 522 ± 20, 522 ± 20, and 489 ± 53 cm^-1, and for NpOH-Ar, NpOH-Ar₂, and NpOH-Ar₃ were 484 ± 8, 572 ± 20, and 461 ± 41 cm^-1, respectively. The corresponding ground-state desorption energies are found to be 10-17 cm^-1 lower, indicating higher adsorption efficiency upon electronic excitation. We further analyzed the impact of substitution, insertion, and ring expansion on adsorption strength. This method offers a versatile and precise spectroscopic tool for quantifying physisorption energies and provides molecular-level insight for designing efficient aromatic adsorbents via noncovalent interactions.