Accurate measurement of sequential Ar desorption energies from the dispersion-dominated Ar1–3 complexes of aromatic molecules

Abstract

We present experimental determination of the energies associated with the gradual desorption of Ar atoms from the aromatic molecular surface. Non-covalently bound 2,2′-pyridylbenzimidazole-Ar_1–3 complexes were produced in the gas phase and characterized using resonant two-photon ionization (R2PI) spectroscopy. The single Ar desorption from the PBI–Ar, PBI–Ar₂ and PBI–Ar₃ complexes were measured as 581 ± 18, 656 ± 30 and 537 ± 31 cm⁻¹, respectively. The energies were bracketed between the last observed band in the respective R2PI spectra and the disappeared intramolecular modes of PBI. The Ar_n dissociation energies in the S₁ state were measured as 581 ± 18, 1237 ± 48 and 1774 ± 79 cm⁻¹, respectively, for n = 1, 2 and 3. The calculated dissociation energies of the respective complexes, obtained using three computational methods, show excellent agreement with the experimental data. The ground state dissociation energies were estimated by subtracting the Δν shift of the origin band, and the respective values are 541 ± 18, 1160 ± 48 and 1634 ± 79 cm⁻¹. Overall, the calculated values resulted in scaling factors ranging from 0.956 to 1.017, which depict the predictive power of the methods to determine dispersion energies. The current investigation describes a unique methodology to accurately determine the dissociation and desorption energies of Ar atoms from the surfaces of bio-relevant aromatic molecules.