The rotational spectra of the HCCCNH+, NCCNH+, and CH3CNH+ ions

The rotational spectra of the HCCCNH+, NCCNH+, and CH3CNH+ ions have been o bserved in a supersonic molecular beam by Fourier transform microwave (FTM) spectroscopy. The rotational and centrifugal distortion constants were det ermined for all three, and the nitrogen quadrupole hyperfine coupling const ants for HCCCNH+ and NCCNH+. From the respective Doppler shifts, it is foun d that the velocities of the ions are 3% larger than those of the parent un protonated molecules, and the linewidths are greater by about 50%. The conc entration of the ions near the nozzle is approximately 10(11) cm(-3), which is sufficiently high to be detectable in the visible and the IR by present laser techniques. (C) 2000 American Institute of Physics. [S0021-9606(00)0 1829-8].