Observation of H2 aggregation onto a doubly charged anion in a temperature-controlled ion trap.

Hydrogen is the second most difficult gas to be condensed due to its weak intermolecular interactions. Here we report observation of H(2) aggregation onto a doubly charged anion, (-)O(2)C(CH(2))(12)CO(2)(-)(DC(2-)). Weakly bound DC(2-)(H(2))(n) clusters were formed in a temperature-controlled ion trap and studied using photoelectron spectroscopy. The onset of clustering was observed at 30 K, whereas extensive condensation was observed at 12 K with n up to 12. Photoelectron spectra were obtained for DC(2-)(H(2))(n) (n = 0-6) at 193 and 266 nm. The spectra of DC(2-)(H(2))(n) were observed to be identical to that of the bare DC(2-) dianion except a slight blue shift, indicating the weak interactions between H(2) and the parent dianion. The blue shift on average amounts to approximately 34 meV (3.3 kJ/mol) per H(2), which represents the lower limit of the H(2) binding energy to DC(2-).