Magnetic Hyperfine Structure in the Rotational Spectrum of H 2 CO

The theory of magnetic hyperfine interaction of an asymmetric rotor molecule with C 2 v symmetry in 1 Σ state was discussed, and the magnetic hyperfine structures in the low frequency rotational spectrum of formalde-hyde were studied with a beam maser. The Δ F =0 and the Δ F =±1 components in the J =4, K -1 =3 and the J =5, K -1 =3 Q -branch transitions were observed with good signal-to-noise ratio. The frequency of the Δ F =0 component of the J =5, K -1 =3 line was measured as 18.275±0.004 Mc. The observed hyperfine structures were analysed with the theory, and the hyperfine coupling constants were determined as α=-13.2±3.4 kc, β=-3.0±3.4 kc and γ=30.2±2.7 kc. The coupling constants were theoretically interpreted, and a proportionality of the hyperfine coupling constans and the rotational g factors for the asymmetric rotor molecule was found. a v arround the proton in H 2 CO was obtained as 1.5×10 24 cm -3 from the comparison of these two quantities.