The Covalent Interaction between Dihydrogen and Gold: a Rotational Spectroscopic Study of H₂-AuCl

The pure rotational transitions of H ₂ -AuCl have been measured using a pulsed-jet cavity Fourier transform microwave spectrometer equipped with a laser ablation source. The structure was found to be T-shaped, with the H-H bond interacting with the gold atom. Both ³⁵ Cl and ³⁷ Cl isotopologues have been measured for both ortho and para states of H2. Rotational constants, quartic centrifugal distortion constants, and nuclear quadrupole coupling constants for gold and chlorine have been determined. The use of the nuclear spin-nuclear spin interaction terms D _aa , D _bb , and D _cc for H ₂ were required to fit the ortho state of hydrogen, as well as a nuclear-spin rotation constant C _aa . The values of the nuclear quadrupole coupling constant of gold are X _aa =-817.9929(35) MHz, X _bb =504.0(27) MHz, and X _cc =314.0(27). This is large compared to the eQq of AuCl, 9.63 312(13) MHz, which indicates a strong, covalent interaction between gold and dihydrogen.