H atom–H2 molecule van der Waals complexes in solid argon matrix by high-resolution ESR spectroscopy

Van der Waals addition complexes of a hydrogen atom with a hydrogen molecule, H–H2, H–HD, H–D2, and D–D2, generated in Ar matrixes have been studied by high-resolution ESR spectroscopy. The complexes were formed by hydrogen atoms migrating in Ar matrices to encounter the hydrogen molecules trapped in the substitutional site. The decay rates of the thermally activated complexes were experimentally determined, and a potential energy of 3.5 kJ mol−1 to stabilize H–H2 complexes was evaluated in the temperature region 24.4–29.3 K. Additionally, the mean distance between the H atom and H2 molecule in the complex was refined to be 0.245 nm by the help of ab-initio MO calculations at the QCISD/aug-cc-pvqz level.