Fourier-transform microwave spectroscopy of the H2–H2O complex

Fourier-transform microwave spectroscopy was applied to observe the J = 1–0 rotational transition of the ortho-H2–H2O complex and isotopologues in the ground Σ0 state (H2 in the jH2 = 1 state and H2O in the ground 000 state) to obtain precise molecular constants. Observed spectra were split into three hyperfine components, confirming the complexes are the ortho-H2/para-D2 species. The determined nuclear spin–spin coupling constant indicates H2 is rotating almost freely in the complex; the Σ0 state is nearly of jH2 = 1 and kH2 = 0. For the ortho-H2 species, the nuclear spin–rotation coupling constant was also determined.