  We suggest a general spectral method for calculating statistics of multi-step
birth-death processes and chemical reactions of the type mA->nA (m and n are
positive integers) which possess an absorbing state. The method yields accurate
results for the extinction statistics, and for the quasi-stationary probability
distribution, including large deviations, of the metastable state. The power of
the method is demonstrated on the example of binary annihilation and triple
branching 2A->0 and A->3A, representative of the rather general class of
dissociation-recombination reactions.
