  We present a theoretical analysis of a microwave spectroscopy experiment on a
charge qubit defined by a P$_2^+$ donor pair in silicon, for which we calculate
Hamiltonian parameters using the effective-mass theory of shallow donors. We
solve the master equation of the driven system in a dissipative environment to
predict experimental outcomes. We describe how to calculate physical parameters
of the system from such experimental results, including the dephasing time,
$T_2$, and the ratio of the resonant Rabi frequency to the relaxation rate.
Finally we calculate probability distributions for experimentally relevant
system parameters for a particular fabrication regime.
