  We explore the appearance of light clusters at high densities of collapsing
stellar cores. Special attention is paid to the unstable isotope H4, which was
not included in previous studies. The importance of light clusters in the
calculation of rates for neutrino matter interaction is discussed. The main
conclusion is that thermodynamic quantities are only weakly sensitive to the
chemical composition. The change in pressure and hence the direct change in
collapse dynamics will be minor. But the change in neutrino heating and
neutronization processes can be significant.
