  We study secondary structures of random RNA molecules by means of a
renormalized field theory based on an expansion in the sequence disorder. We
show that there is a continuous phase transition from a molten phase at higher
temperatures to a low-temperature glass phase. The primary freezing occurs
above the critical temperature, with local islands of stable folds forming
within the molten phase. The size of these islands defines the correlation
length of the transition. Our results include critical exponents at the
transition and in the glass phase.
