The photoelectron (PE) spectra of some ortho-disubstituted quinoxalines were measured and assigned mainly on the basis of HAM/3, INDO, and CNDO MO calculations. In the case of cNoro derivatives, the given assignment takes also into account the arguments based on a comparison of HeIUHeI intensities.

The He1 photoelectron (PE) spectra of six 4-substituted 3-methyl-I-phenylpyrdzolin-5-ones and the unsubstituted parent compound were measured. The interpretation of the low-energy region of these spectra is attempted on the basis of HAM/3 molecular orbital calculations, making allowance for different tautomeric forms of the compounds. The results indicate preference of the CH versus the NH and/or OH tautomers of these compounds in the gas phase at the temperatures employed ( 100-1 50°C).