A new technique for state-to-state studies of unimolecular reactions

A double-resonance technique which combines infrared excitation of a fundamental vibration of a light atom oscillator with vibrational overtone excitation of that same oscillator selectively prepares molecules in individual quasibound vibrational–rotational states at energies above their dissociation threshold. A third laser probes individual states of the product fragments via laser induced fluorescence. We present our initial results applying this technique to study the 6νOH vibrational overtone spectroscopy and unimolecular dissociation dynamics of hydrogen peroxide (HOOH). The double-resonance approach simplifies the congested vibrational overtone spectrum of HOOH, and the linewidth of resolved features places a lower limit on the lifetime of approximately 7 ps.