Selective infrared laser pulses in the femtosecond (fs) time domain may be used to prepare quasi-coherent molecular vibrations in the dissociative continuum of the ground electronic state. These vibrations may be monitored by femtosecond IR+UV pump-probe spectroscopy. The new phenomenon is discovered by means of molecular wave-packet simulations for a two-dimensional model based on ab initio potential-energy surfaces and dipole functions for HONO2.