  The 15O(alpha,gamma)19Ne reaction is one of two known routes for breakout
from the hot CNO cycles into the rp process. Its astrophysical rate depends on
the decay properties of excited states in 19Ne lying just above the 15O + alpha
threshold. We have measured the alpha-decay branching ratios for these states
using the p(21Ne,t)19Ne reaction at 43 MeV/u. Combining our branching ratio
measurements with previous determinations of the radiative widths of these
states, we calculate the astrophysical rate of 15O(alpha,gamma)19Ne. Using this
reaction rate, we perform hydrodynamic calculations of nova outbursts and
conclude that no significant breakout from the hot CNO cycles into the rp
process occurs in classical novae via 15O(alpha,gamma)19Ne.
