Morphing the ground state potential of the hydrogen-bonded complex HBr-HBr

Rotational-tunneling transitions including quadrupole substructure in H79Br-H79Br, H79Br-H81Br, and H81Br-H81Br have been recorded and assigned. When combined with previously recorded rovibrational infrared and microwave data, this provides a basis for optimizing a ground state four-dimensional morphed potential with quantifiable uncertainties. The determined potential minimum has a value V = −644.0 cm−1 at the geometry R = 4.04 Å, θ1 = 16.9°, θ2 = 108.3°, and ϕ = 180.0°. The peak of the minimum energy path between the two equivalent minima occurs at V = −571.2 cm−1, leading to a barrier height of 72.8 cm−1.