  We present a method to sample reactive pathways via biased molecular dynamics
simulations in trajectory space. We show that the use of enhanced sampling
techniques enables unconstrained exploration of multiple reaction routes. Time
correlation functions are conveniently computed via reweighted averages along a
single trajectory and kinetic rates are accessed at no additional cost. These
abilities are illustrated analyzing a model potential and the umbrella
inversion of NH$_3$ in water. The algorithm allows a parallel implementation
and promises to be a powerful tool for the study of rare events.
