Emission spectra of the cations of cyanodiacetylene, methylcyanodiacetylene and ethylcyanodiacetylene in the gaseous phase. Ã(π–1)→X (π–1) band systems

Abstract

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 òΠ→X²Π, òE→X²E and òA″→X²A″ 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 X(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.