Time-resolved optical double resonance spectroscopy in acetylene : exploring rovibrational energy transfer at various levels of excitation

Abstract

Time-resolved optical double resonance (DR) techniques are useful not only for high-resolution spectroscopy, but also for studies of the mechanisms by which molecules transfer energy from one distinct rovibrational quantum state to another, thereby elucidating aspects of chemical reactivity and energetics. The DR approach employs tunable laser excitation to prepare a molecule in a specific state and a second laser absorption step either to characterise that excitation or to probe resulting state-to-state molecular energy transfer. Typically, we use either infrared (IR) absorption or coherent Raman excitation for state preparation and ultraviolet (UV) laser-induced fluorescence (LIF) for detection. The emphasis in this work is on high state-specificity and sensitivity, to enable detailed modeling of the resulting spectroscopic and kinetic data and to provide insight into the intermolecular and intramolecular energy transfer processes involved. Figure 1 depicts the LIF-detected Raman-UVDR and IRUVDR excitation schemes.