  We consider the time evolution of a particle subjected to both a uniform
electrostatic field F and a one-dimensional delta-function potential well. We
derive the propagator K_F(x,t|x',0) of this system, directly leading to the
wavefunction psi_F(x,t), in which its essential ingredient K_F(0,t|0,0),
accounting for the ionization-recombination in the bound-continuum transition,
is exactly expressed in terms of the multiple hypergeometric functions
F(z_1,z_2,...,z_n). And then we obtain the ingredient K_F(0,t|0,0) in an
appropriate approximation scheme, expressed in terms of the generalized
hypergeometric functions p_F_q(z) being much more transparent to physically
interpret and much more accessible in their numerical evaluation than the
functions F(z_1,z_2,...,z_n).
