Microwave spectra and structure of HI-HF complexes

Microwave spectra for the HI-HF, HI-DF, DI-HF, and DI-DF complexes were measured using a pulsed-beam, Fourier-transform microwave spectrometer. Rotational transitional transitions were measured over the 4-18 GHz range to an accuracy of 5 kHz. The spectroscopic constants obtained by fitting the observed transitions for the series HI-HF, HI-DF, DI-HF, and DI-DF are, respectively: (B+C)/2=2220.7482(8), 2173.236(2), 2209.623(4), and 2162.884(6) MHz; eQq(I)=687.01(2), 693.63(5), 725.96(4), and 727.8(1) MHz; ΔeQg(I)=-42(2), -50(6), -210(14), and -141(25) kHz; D_J=8.86(3), 8.25(6), 8.1(6), and 8.6(5) kHz. This complex has an interesting triangular structure with the H-I and H-F bonds making an acute angle of 70.1 (2.8)°. The iodine atom is coaxial with HF with a heavy atom separation R₀(I-F)=3.660(8) Å. Hyperfine structure due to deuterium quadrupole coupling and H-F spin-spin interactions was resolved and measured.