The photoionization of a series of ketones, acetone, 2hyphen;butanone, 2hyphen;pentanone, 3hyphen;methylhyphen;2hyphen;butanone, 2hyphen;hexanone, and 4hyphen;methylhyphen;2hyphen;pentanone was studied using mass spectrometric techniques. Adiabatic ionization potentials were determined. It was found that for the ketones the cross section above threshold is not constant, and a modified method of treatment of the results was developed in order to obtain information about fragmentation processes. The shifts in appearance potentials of fragments with increasing temperature were found to be close to the change in internally stored energy. Bond dissociation energies in ions were calculated. The adiabatic ionization potential of the acetyl radical was calculated to be 7.08 eV, which is considerably lower than reported by authors using electron impact where no effort was made to distinguish between adiabatic and vertical ionization potentials. A lower limit was calculated for the ionization potential of thenhyphen;propyl radical leading to a value of the adiabatic ionization potential of 7.2plusmn;0.2 eV.
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