Laser-induced fluorescence of matrix-isolated HCCCCCN+ and HCCCCCCCN+

The cyanodiacetylene (HC5N+) and cyanotriacetylene (HC7N+) cations were produced in a pulsed supersonic discharge through a dilute cyanoacetylene (HC3N) neon mixture, and isolated in solid neon at 5–7 K. The A2Π-X2Π transitions of these cations were investigated by means of laser excitation and Fourier-transform emission spectroscopy. New ground-state vibrational information is obtained for HC5N+ and HC7N+. The latter is identified with the help of a particle-in-a-box model of electronic transition energies of these long-chain linear ions. Its identity is confirmed by analysis of the observed vibronic structure. Interesting matrix site effects lead to the observation of the ΔΩ = ± 1 transitions for one of the two sites. These yield the spin-orbit splitting constants A00 = 92 cm−1and A0 = 17 cm−1 for HC5N+ and A00 = 91 cm−1 and A0 = 19 cm−1 for HC7N+.