Rotationally resolved vibrational overtone spectroscopy of hydrogen peroxide at chemically significant energies

Abstract

An infrared–optical double resonance scheme simplifies the room temperature 6νOH vibrational overtone spectrum of hydrogen peroxide and prepares highly excited reactant molecules in single rotational states for unimolecular reaction studies. First, an optical parametric oscillator excites the OH asymmetric stretch (ν5) and selects a single or small subset of rotational states. A visible dye laser pulse then promotes molecules from vOH=1 to vOH=6 where they subsequently dissociate to produce two OH fragments. A third laser detects the dissociation products via laser induced fluorescence. The rotationally resolved vibrational overtone spectra of hydrogen peroxide generated by scanning the visible dye laser frequency are assignable to a parallel band of a near prolate symmetric top. Linewidths of the individual rovibrational features range from 1–3 cm−1 but show no systematic dependence upon the rotational quantum numbers and are attributed predominantly to anharmonic coupling of the zeroth-order bright state to dark background states. The assignability of the double-resonance vibrational overtone spectra to J and K quantum numbers implies that K is conserved for at least a time determined by the linewidth of a single zeroth-order rovibrational feature.