More than 100 excited states of the Calcium-40 nucleus, with isospin 0, are classified into rotational–vibrational bands of an intrinsic tetrahedral structure. Almost all observed states below 8Formula: see textMeV can be accommodated, as well as many high-spin states above 8Formula: see textMeV. The bands have some similarity to those classifying states of Oxygen-16, but the A-mode vibrational frequency is lower relative to the E-mode and F-mode frequencies than in Oxygen-16. Previously identified rotational bands up to spin 16 and energy above 20Formula: see textMeV are unified here into a smaller number of tetrahedral bands.
NS Manton (2026) studied this question.