LOCAL MODES OF HOOH PROBED BY OPTICAL-INFRARED DOUBLE-RESONANCE

We have used an optical-infrared double resonance technique to probe the nature of the eigenstates prepared by 4-nu-OH vibrational overtone excitation in hydrogen peroxide. A visible dye laser excites the 4 <-- 0 OH stretch transition and an optical parametric oscillator promotes the molecules above the dissociation threshold by a DELTA-upsilon-OH = 2 transition from the 4-nu-OH level. Fixing the overtone excitation laser wavelength and scanning the wavelength of the infrared photon while monitoring the dissociation fragments by laser-induced fluorescence generates an infrared predissociation spectrum of the vibrationally excited molecule that contains information about vibrational state mixing at the 4-nu-OH level. This spectrum indicates that the zeroth-order state that gives oscillator strength to the 4 <-- 0 OH stretch transition (i.e., the 4-nu-OH bright state) is almost entirely comprised of a single vibrational eigenstate. Since the bright state is predominantly an OH stretch, the vibrational eigenstate prepared by 4-nu-OH vibrational overtone excitation is well localized on the OH bond. This localization allows us to perform sequential local mode-local mode excitation of the two equivalent OH oscillators in HOOH.