Accurate measurement of sequential Ar desorption energies from the dispersion-dominated Ar1-3 complexes of 1-naphthol

We devise a unique experimental methodology to accurately measure the sequential desorption of Ar atoms from the aromatic surface of 1-naphthol (NpOH). The dispersion-dominated NpOH·Ar1-3 complexes were characterized using resonant two-photon ionization (R2PI) spectroscopy in the gas phase. The band origins 〖(0〗_0^0) for S1←S0 transition in the NpOH·Ar, NpOH·Ar2 and NpOH·Ar3 complexes were observed at 31440, 31425 and 31415 cm-1, respectively. The above values were red-shifted by 15, 30 and 40 cm-1 () compared to that of the NpOH (0_0^0 at 31455 cm-1) molecule. The disappearance of Franck-Condon active vibrational bands in the R2PI spectrum was utilized to determine the D0(S1) values of non-covalently bound molecular complexes. The single Ar desorption energies from the NpOH·Ar, NpOH·Ar2 and NpOH·Ar3 complexes were measured as 487 5, 471 21 and 442 24 cm-1, respectively. The corresponding dissociation energies D0(S1) were measured as 487 5, 958 26 and 1400 50 cm-1. The D0(S0) values were determined by subtracting the shift of the origin band, and the respective values are 472 5, 928 26 and 1360 50 cm-1. The preferable orientation for the efficient desorption was obtained with the first Ar atom positioned on the top face of the NpOH ring. A second Ar atom was bound to the bottom face of the NpOH ring. The docking of third Ar atom could be on the NpOH face above OH (I1), CH (I2) or π (I3), as all these structures are isoenergetic to each other. The best correlation of the experimental and calculated dissociation energies of NpOH·Ar1-3 (I1) complexes is obtained at the B-LYP-D4/def2-TZVPP level of theory, with an accuracy of 3-5%. The current study provides an inexpensive laser spectroscopic method to precisely determine the dissociation energies of the dispersively bound complexes of biorelevant aromatic molecules based on their Franck-Condon activity