Molecular g-Value Tensor, the Molecular Susceptibility Tensor, and the Sign of the Electric Dipole Moment in Formaldehyde

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Abstract
The diagonal elements in the molecular g‐value and magnetic‐susceptibility tensors in the principal inertial axis in formaldehyde have been determined by observing the molecular rotational Zeeman effect. A small J dependence was observed in the molecular g values where the absolute values increased with rotational excitation. The g values averaged over the three rotational states studied for each isotopic species are g aa = − 2.899 ± 0.002 , g bb = − 0.2256 ± 0.0008 , and g cc = − 0.1004 ± 0.0007 for H2CO, and g aa = − 1.445 ± 0.002 , g bb = − 0.1917 ± 0.0005 , and g cc = − 0.0788 ± 0.0004 for D2CO. The diagonal elements in the molecular magnetic‐susceptibility tensor are χ aa = − 6.2 ± 0.5 , χ bb = − 15.8 ± 0.4 , and χ cc = − 23.0 ± 0.4 , all in units of 10−6erg/G2·mole. The sign of the electric dipole moment along the C‐O bond in formaldehyde was determined to have +C‐O− polarity from the isotope dependence in the above molecular g values. From the g values and the known structure of formaldehyde, the paramagnetic‐susceptibility tensor elements can be calculated to be χ aa p = 29.5 ± 0.1 , χ bb p = 46.1 ± 0.5 , and χ cc p = 47.7 ± 0.5 , all in units of 10−6erg/G2·mole. These data, combined with our above experimental magnetic‐susceptibility diagonal tensor elements give the experimental ground‐state average values of the sums of squared Cartesian center‐of‐mass electronic coordinates. The results are 〈0 | Σ i x i 2 | 0〉 = (3.2 ± 0.3) Å 2 , 〈0 | Σ i y i 2 | 0 = (5.2 ± 0.3) Å 2 , and 〈0 | Σ i z i 2 | 0〉 = (11.4 ± 0.3) Å 2 . The z axis is along the O‐C bond and the y axis is in the molecular plane. These new data are used to interpret the ground‐ and excited‐state electronic structure of the formaldehyde molecule. The experimental information is also sufficient to determine the diagonal elements in the molecular quadrupole moment tensor.