  We examine a square-lattice nearest-neighbor Ising quantum ferromagnet
coupled to $d$-dimensional phonon baths. Using the density-matrix equation, we
calculate the transition rates between configurations, which determines the
specific dynamic. Applying the calculated stochastic dynamic in Monte Carlo
simulations, we measure the lifetimes of the metastable state. As the magnetic
field approaches $|H|/J=2$ at low temperatures, the lifetime prefactor diverges
because the transition rates between certain configurations approaches zero
under these conditions. Near $|H|/J=2$ and zero temperature, the divergent
prefactor shows scaling behavior as a function of the field, temperature, and
the dimension of the phonon baths. With proper scaling, the simulation data at
different temperatures and for different dimensions of the baths collapse well
onto two master curves, one for $|H|/J>2$ and one for $|H|/J<2$.
