Band analysis of the Swan system ( d3Π g- a3Π u) of 13C 2 and 12C 13C molecules

The emission spectrum of the d³Π _g- a³Π _u system (Swan bands) due to ¹³C ₂ and ¹²C ¹³C molecules has been obtained in a low pressure hollow cathode discharge through a mixture of argon and benzene containing enriched ¹³C (90%). The spectrum was photographed on a 3.4-m Ebert spectrograph (reciprocal dispersion 0.54 Å mm ^-1 in the first order). Isotope effect measurements have been carried out to determine the shift between isotopic bands and those emitted by ordinary molecules. The rotational analysis of six ¹³C ₂ bands and three bands of ¹²C ¹³C has been performed and molecular constants were derived.