Measurements of deuterium quadrupole coupling in propiolic acid and fluorobenzenes using pulsed-beam Fourier transform microwave spectrometers

The pure rotational spectra of deuterated propiolic acids (HCCCOOD and DCCCOOH), 1-fluorobenzene (4-d₁), and 1,2-difluorobenzene (4-d₁) in their ground states have been measured using two Fourier transform microwave (FTMW) spectrometers at the University of Arizona. For 1-fluorobenzene (4-d₁), nine hyperfine lines of three different ΔJ = 0 and 1 transitions were measured to check the synthesis method and resolution. For 1,2-difluorobenzene (4-d₁), we obtained 44 hyperfine transitions from 1 to 12 GHz, including 14 different ΔJ = 0, 1 transitions. Deuterium quadrupole coupling constants along the three principal inertia axes were well determined. For deuterated propiolic acids, 37 hyperfine lines of Pro-OD and 59 hyperfine lines of Pro-CD, covering 11 and 12 different ΔJ = - 1, 0, 1 transitions, respectively, were obtained from 5 to 16 GHz. Deuterium quadrupole coupling constants along the three inertia axes were well resolved for Pro-OD. For Pro-CD, only eQq_aa was determined due to the near coincidence of the CD bond and the least principal inertia axis. Some measurements were made using a newer FTMW spectrometer employing multiple free induction decays as well as background subtraction. For 1-fluorobenzene (4-d₁) and 1,2-difluorobenzene (4-d₁), a very large-cavity (1.2 m mirror dia.) spectrometer yielded very high resolution (2 kHz) spectra.