The two-point correlation functions of energy levels for free motion o
n the modular domain, both with periodic and Dirichlet boundary condit
ions, are explicitly computed using a generalization of the Hardy-Litt
lewood method. It is shown that in the limit of small separations they
show an uncorrelated behaviour and agree with the Poisson distributio
n but they have prominent number-theoretical oscillations at larger sc
ale. The results agree well with numerical simulations.