Fourier-transform microwave spectroscopy of the H2–HCN complex

Fourier-transform microwave spectroscopy was applied to observe the J = 1–0 rotational transition of the H2–HCN complex for both the ortho- and para-H2 species to obtain improved molecular constants by an analysis combined with the millimeter-wave data. It was confirmed that the para- and ortho-H2 species have different configurations: namely H2 is attached to the H end of HCN in the former, while to the N end in the latter. For the ortho-H2 species, the hyperfine splitting due to the magnetic interaction between the hydrogen nuclei was observed to give the nuclear spin–spin coupling constant dH = 54.6(38) kHz.