  The $\alpha$ particle and $^6$He emissions from possible molecular states in
beryllium and carbon isotopes have been studied using a mean-field-type cluster
potential. Calculations can reproduce well the $\alpha$-decay widths of excited
states in $^{8}$Be, $^{12}$C and $^{20}$Ne. For the nucleus $^{10}$Be, we
discussed the $\alpha$-decay widths with different shapes or decay modes, in
order to understand the very different decay widths of two excited states. The
widths of $^{6}$He decay from $^{12}$Be and $\alpha$ decays from $^{13,14}$C
are predicted, which could be useful for future experiments.
