The emission spectra of the cations of cyanodiacetylene, methylcyanodiacetylene and ethylcyanodiacetylene have been detected using low energy electron beam excitation. The emission band systems lie in the 550-670 nm wavelength region and are assigned to the Ã2Π→text-decoration:overlineX2Π, Ã2E→text-decoration:overlineX2E and Ã2A″→text-decoration:overlineX2A″ electronic transitions of these three cations, respectively. This follows from the photoelectron spectra of these compounds, which have also been obtained, and from their assignment. The vibrational frequencies (± 10 cm–1) of four or five of the totally symmetric fundamentals of the three cyanodiacetylene cations in the text-decoration:overlineX(π–1) states have been inferred from the vibrational analyses of the emission spectra. These frequencies are supplemented by values (± 160 cm–1) obtained for the Ã(π–1) states from the photoelectron spectra. The lifetimes of the title cations in the lowest vibrational level of their à states have been measured as 15 ± 2, 8 ± 2 and ⩽ 6 ns, respectively.
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Bieri et al. (1980) studied this question.