Infrared spectroscopy
Infrared spectroscopy of molecular UO3 isolated in an argon matrix indicates a T-shaped structure (point group "C2v") for the molecule. This is in contrast to the commonly encountered "D3h" molecular symmetry exhibited by most trioxides. From the force constants the authors deduct the U-O bond lengths to be between 1.76 and 1.79 Å (176 to 179 pm).