Polarizability of a single hydrogen atom

[Cranky]

Homework Statement

the problem text is attached

Homework Equations

The Attempt at a Solution

I have solved Schrödingen equation, while getting
psi(x)=c1*cos(kx)+c2*sin(kx), where k=sqrt(2Em)/hbar
I cannot understand which boundary conditions I schould use.

 

[Western38]

Bump; is the approach to use perturbation theory with the Stark effect?