Influence of initial parent vibrational excitation in promoting two-photon absorption in HOOH and CH3OOH

Two-photon dissociation of vibrationally excited HOOH and CH3OOH is demonstrated from their 2νOH stretching overtone state using ∼205 nm light. Initial vibrational excitation appears to be a prerequisite for accessing the two-photon excited dissociative electronic state in these hydroperoxides, most likely due to the ability of vibrational excitation to improve the Franck-Condon factor. The hydroperoxide excited state accessed through the vibrationally mediated photodissociation process generates OH fragments in their A2Σ+ electronic excited state. Detection of the OH(A2Σ+) fluorescence as a function of the vibrational excitation laser allows recording of the 2νCH overtone action spectra for CH3OOH with high sensitivity.

Graphical abstractDownload high-res image (77KB)Download full-size imageHighlights► Influence of vibrational excitation on two-photon absorption. ► Action spectroscopy via two-photon vibrationally mediated photodissociation (VMP). ► 2νOH overtone spectra of HOOH and CH3OOH via two-photon VMP. ► 2νCH overtone spectra of CH3OOH via two-photon VMP.