The HeI photoelectron spectra of fluoroacetone, 1,1,1hyphen;trifluoroacetone, 1,1,1hyphen;trichlorotrifluoroacetone, 1,1,3hyphen;trichlorotrifluoroacetone, 1,1,3,3hyphen;tetrafluoroacetone, 1hyphen;chlorohyphen;1,1,3,3hyphen;tetrafluoroacetone, chloropentafluoroacetone, chloroacetone, and 3hyphen;bromohyphen;1,1,1hyphen;trifluoroacetone have been determined and the vertical ionization energies measured. They have been compared with ionization energies calculated by CNDO/2 and MO assignments of the bands have been made on this basis. A correlation between the oxygen lone pair ionization energy and the number of fluorines substituted was observed. This paralleled a correlation between the width at halfhyphen;peak height of the lone pair band and the lone pair ionization energy. The carbonyl stretching frequencies were determined and also found to correlate with the oxygen lone pair ionization energy. The linear plot suggested that the oxygen lone pair ionization energies are related to the sum of the effective electronegativities of the substituents. The first chlorine lone pair ionization energy and the carbonyl pgr; were investigated to see if their ionization energies are related to the sum of the effective electronegativities of the substituents. In all three cases, an empirical relationship,IE= agr; (XA+XB)+bgr;, was found to hold where agr; and bgr; are constants determined by least squares fit of the data and whose value depends on the type of orbital considered. The values of agr; and bgr; for the oxygen lone pairs of halogen substituted acetones were found to be 1.24 and 3.91, respectively. For the chlorine lone pairs, the values were found to be 1.16 and 5.89, while for the carbonyl pgr;, they were found to be 1.98 and 3.17, respectively.
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