The "molecular" charmonium models predict both $I=0$ and $I=1$ states. The closeness of one of these (4.028 GeV) to one of its main thresholds and the large electromagnetic mass splitting of its daughters may induce a large mixing between states of different isospin. This would manifest itself in deviations from unity of the ratio of charged to neutral decay modes.

• Received 21 June 1977

DOI:https://doi.org/10.1103/PhysRevD.16.2900