So, dissociation involves, increasing the energy of the system from the zero point energy, up to zero, so the bond breaks.
the zero point energy is 1/2 hbar W for a harmonic oscillator.
W= (k/m)^1/2 where m is the reduced mass of the system
so for H2 you can work out what the ground state energy is in terms of k.
k is the bond force constant, and is the same for H2 and HD so jus tthe change in mass needs to be accounted for.
you'll find that HD has a smaller zero point energy and hence more energy is required to dissociate HD, this is the origin of the primary kinetic isotope effect!
hopefully that info will allow you to work out the answer