Molecular forms Uranium trioxide

1 molecular forms

1.1 gas phase
1.2 matrix isolation
1.3 computational study

molecular forms

while uranium trioxide encountered polymeric solid under ambient conditions, work has been done on molecular form in gas phase, in matrix isolations studies, , computationally.

gas phase

at elevated temperatures gaseous uo3 in equilibrium solid u3o8 , molecular oxygen.

2 u3o8(s) + o2(g) ⇌ 6 uo3(g)

with increasing temperature equilibrium shifted right. system has been studied @ temperatures between 900 °c , 2500 °c. vapor pressure of monomeric uo3 in equilibrium air , solid u3o8 @ ambient pressure, 10 mbar (1 mpa) @ 980 °c, rising 0.1 mbar (10 pa) @ 1400 °c, 0.34 mbar (34 pa) @ 2100 °c, 1.9 mbar (193 pa) @ 2300 °c, , 8.1 mbar (809 pa) @ 2500 °c.

matrix isolation

infrared spectroscopy of molecular uo3 isolated in argon matrix indicates t-shaped structure (point group c2v) molecule. in contrast commonly encountered d3h molecular symmetry exhibited trioxides. force constants authors deduct u-o bond lengths between 1.76 , 1.79 Å (176 179 pm).

computational study

the calculated geometry of molecular uranium trioxide has c2v symmetry.

calculations predict point group of molecular uo3 c2v, axial bond length of 1.75 Å, equatorial bond length of 1.83 Å , angle of 161° between axial oxygens. more symmetrical d3h species saddle point, 49 kj/mol above c2v minimum. authors invoke second-order jahn–teller effect explanation.