Question 2.19:

If one of the two electrons of an H2 molecule is removed, we get a hydrogen molecular ion H:. In the ground state of an H2+, the two protons are separated by roughly 1.5 A, and the electron is roughly 1 Å from each proton. Determine the potential energy of the system. Specify your choice of the zero of potential energy.

 
The system of two protons and one electron is represented in the given figure. - 1.6 x 10-19C
Charge on proton 1, q1 = 1.6 X 10-19C
Charge on proton 2, q2 = 1.6 X 10-19C
Charge on electron, q3 = -1.6 x 10-10 m
Distance between protons 1 and 2, d1 = 1.5 x 10-10
Distance between proton 1 and electron, d2 1 x 10-10 m Distance 
between proton 2 and electron, d3 = 1 x 10-10 m
The potential energy at infinity is zero.
The potential energy of the system, 
V=q1q24πϵ0d1+q2q34πϵ0d3+q3q14πϵ0d2 Substituting 14πϵ0=9×10Nm2C2,we obtain 
V=9×109×1019×10191010[(16)2+(1.6)21.5+(1.6)2]=30.7×1019 J=19.2eV
Therefore, the potential energy of the system is -19.2 ev.