Spectroscopic identification of higher-order rare gas-dihalogen complexes with different geometries: He_2,3...Br₂ and He _2,3.....ICl

Rovibronic transitions of multiple conformers of the He₂..... ⁷⁹Br₂X, v = 0), He₃....⁷⁹Br ₂(X, v = 0), He₂...I³⁵Cl(X, v = 0), and He ₃.....I³⁵Cl(X, v = 0) complexes stabilized in a pulsed, supersonic expansion are observed in action spectra recorded in the B-X region of the dihalogens. In addition to features associated with He₂.. ⁷⁹Br₂ and He₂....I³⁵Cl complexes with the rare gas atoms localized in the toroidal potential well lying in a plane perpendicular to the dihalogen bond, those associated with a ground-state conformer that has one He atom localized in the toroidal potential and the other He atom localized in the linear well at the end of the dihalogen moiety are also identified. Transitions of at least three conformers of the He ₃...Br₂ complex and two conformers of the He ₃···ICl complex are also observed. The relative populations of the different conformers are found to depend on where along the supersonic expansion the spectra are recorded, and thus on the local temperature regime sampled. The He₂....I⁷⁹Br₂ and He ₂....I³⁵Cl conformers with one He atom in each well are found to be the more stable conformers.