Infrared spectra of Rg1,2-C6H6 complexes, Rg = He, Ne, Ar

Electronic and vibrational spectroscopies of aromatic clusters with He in a supersonic jet: The case of neutral and cationic phenol-Hen (n = 1 and 2)

Van der Waals clusters composed of He and aromatic molecules provide fundamental information about intermolecular interactions in weakly bound systems. In this study, phenol-helium clusters (PhOH-Hen with n ≤ 2) are characterized for the first time by UV and IR spectroscopies. The S1 ← S0 origin and ionization energy both show small but additive shifts, suggesting π-bound structures of these clusters, a conclusion supported by rotational contour analyses of the S1 origin bands. The OH stretching vibrations of the PhOH moiety in the clusters match with those of bare PhOH in both the S0 and D0 states, illustrating the negligible perturbation of the He atoms on the molecular vibration. Matrix shifts induced by He attachment are discussed based on the observed band positions with the help of complementary quantum chemical calculations. For comparison, the UV and ionization spectra of PhOH-Ne are reported as well.

Many-Body Dispersion

A broad range of approaches to many-body dispersion are discussed, including empirical approaches with multiple fitted parameters, augmented density functional-based approaches, symmetry adapted perturbation theory, and a supermolecule approach based on coupled cluster theory. Differing definitions of "body" are considered, specifically atom-based vs molecule-based approaches.

Quantum Tunneling of a He Atom Above and Below a Benzene Ring

Van der Waals (vdW) complexes with helium atoms have deserved much attention for their intriguing quantum nature relevant to microscopic superfluidity. However, tunneling splitting, the clear signature of quantum delocalization of He atoms, has rarely been identified in any of the He-containing complexes. Here, UV excitation spectra of benzene-He were extensively examined with almost full rotational resolution to identify two weak vibronic bands with vibrational excitation energies of only ∼13 and ∼16 cm^-1. Each of rotational transitions appears to be split into doublets in the higher-frequency band. This splitting is attributed to quantum tunneling due to the delocalization of He spread over two minimum locations below and above the benzene ring. The magnitude of the tunneling splitting as well as the vibrational frequencies of the two vdW modes are compared with the reported theoretical prediction to quantitatively assess the intermolecular potential energy surfaces so far derived.