Dissociative photoionization of CH3C(O)CH2 to C2H5+

We use a combination of crossed laser-molecular beam scattering experiments and velocity map imaging experiments to investigate the dissociative ionization of the CH3C(O)CH2 radical to C2H5+. We form the radical from C–Cl bond fission in the photodissociation of chloroacetone at 193 nm. Upon 10.5 eV VUV photoionization, the radical is not detected at a parent mass-to-charge ratio of 57, but instead is only detected at the fragment m/z = 29 (C2H5+). While the appearance of multiple daughter ions is expected, and indeed observed, using 200 eV electron bombardment ionization, one normally expects “soft” VUV photoionization to give signal at parent ion. We present electronic structure calculations that offer an explanation of our experimental results. The results presented herein also confirm the presence of a minor dissociation channel for the highly vibrationally excited CH3C(O)CH2 radicals – one that forms C2H5 + CO following isomerization to CH3CH2CO.

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► 10.5 eV ionization of CH3C(O)CH2 yields C2H5+ fragments rather than parent ions.
► Our results characterize the efficient dissociative ionization of CH3C(O)CH2 to m/z = 29.
► A minor dissociation channel of CH3C(O)CH2 is confirmed, that to C2H5 + CO.
► For this system, there are 2 sources of m/z = 29, not just the ionization of C2H5.
► Care should be taken in assigning m/z = 29 signal in multicomponent systems.