Vibrational overtone spectroscopy of bound and predissociative states of hydrogen peroxide cooled in a supersonic expansion

The vibrational overtone excitation spectra of both bound and predissociative states of hydrogen peroxide molecules cooled in a supersonic expansion show features that are obscured otherwise. Spectra of predissociative states are measured by detecting the decomposition product following excitation of an overtone vibration. Spectra of bound states are obtained by a two‐photon excitation technique in which a second photon excites the molecule from its bound vibrational overtone state to a dissociative state. The features in the bound state (4ν_OH) spectrum are 0.08 to 0.13 cm⁻¹ wide, reflecting small inhomogeneous broadening, but those to the predissociative state (6ν_OH) are 1.5±0.3 cm⁻¹ wide. This width, which corresponds to a lifetime of about 3.5 ps, reflects coupling into the dissociative continuum.