We have carried out semi-empirical quantum mechanical molecular dynamics (MD) simulations involving collisions of two pentaerythritol tetranitrate (PETN) molecules at different molecular orientations and at several intermolecular separations. The common features of reactive scattering among all molecular orientations are (1) the dissociation mechanism of PETN remains unimolecular and (2) the dominant reaction channel is the breaking of an O-NO2 bond. However, the probability of collision-induced decomposition of PETN depends strongly on initial conditions, in agreement with the experimentally observed sensitivity of shock-initiated detonation in bulk PETN along different crystalline orientations. In addition, the next most frequent reaction path shows a dependence on initial orientations.