Production of CH(X2Π) from the multiphoton dissociation of CH2CO at wavelengths of 279.3 and 308 nm

Abstract

CH(X²Π) has been observed by laser-induced fluorescence (LIF) spectroscopy as the product of the two-photon dissociation of ketene (CH₂CO) at 279.3 and 308 nm. The nascent distribution of rotational levels is Gaussian in profile, consistent with a ‘rotational reflection’ principle in the dissociation. Thermodynamic arguments imply a fragmentation pathway to CH + HCO following an initial one-photon absorption to the ¹A″ excited state of ketene, a second photon absorption, and dissociation following rearrangement via a formylmethylene isomer. Analysis of Λ doublets in the LIF spectra shows no orbital alignment of CH produced on photolysis at 279.3 nm, but some propensity for Π(A′) symmetry alignment (π orbital of CH parallel to the plane of rotation) for photolysis at 308 nm.