STUDIES OF C 1S-]PI-ASTERISK TRIPLET-STATES OF CARBON-MONOXIDE, BENZENE, ETHYLENE, AND ACETYLENE

The (C 1s(-1),pi) triplet states of carbon monoxide, benzene, ethylen e, and acetylene have been studied using electron energy loss spectros copy with low-energy (near-threshold) excitation. The singlet-triplet splitting for the (C 1s(-1), pi) states of the hydrocarbon species we re measured for the first time. Intermediate neglect of differential o verlap (spectroscopic) (INDO/S) calculations within the equivalent cor es approximation were used to calculate (1s(-1), pi) singlet-triplet splittings. The calculated values are in reasonable agreement with the experimental values for the hydrocarbon species but are significantly underestimated for CO. A strong correlation between singlet-triplet s plittings and oscillator strengths for the 1s --> pi transitions was noted and rationalized in terms of the dependence of both factors on t he spatial overlap of 1s and pi wave functions.