Quadrupole Arrangements in Solid CO

The group-theoretical classification of all possible quadrupole arrangements which was carried out in a previous paper for crystals such as H₂ and N₂ is extended here to include CO, the molecules of which lack a center of symmetry. It turns out that the quadrupole arrangement in the cubic phase is T⁴ with axially symmetric quadrupoles. From symmetry considerations of the quadrupoles only, it is shown that a structure similar to the tetragonal D₄ₕ¹⁴ arrangement in γ nitrogen cannot be formed in solid CO, in accord with recent experimental results.