PNNL

Abstract

Hydrogen is the second most difficult gas to be condensed due to its weak intermolecular interactions. Here we report observation of H2 aggregation onto a doubly charged anion, –O2C(CH2)12CO2– (DC2–). Weakly-bound DC2–(H2)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 DC2–(H2)n (n = 0–6) at 193 and 266 nm. The spectra of DC2–(H2)n were observed to be identical to that of the bare DC2– dianion except a slight blue shift, indicating the weak interactions between H2 and the parent dianion. The blue shift on average amounts to ~34 meV (3.3 kJ/mol) per H2, which represents the lower limit of the H2 binding energy to DC2–.