Molecular Beam Measurement of the Magnetic Susceptibility Anisotropies and Molecular Quadrupole Moment in H2CO

Abstract

The molecular Zeeman effect in formaldehyde was studied using a molecular beam maser spectrometer in fields to 17 kG. The molecular resonance linewidth was 5 kHz. $\text{ΔM\hspace{0.17em}=\hspace{0.17em}0}$ and $\text{ΔM\hspace{0.17em}=\hspace{0.17em}±\hspace{0.17em}1}$ transitions were observed for the 1₁₀ → 1₁₁ rotational transition. The measured susceptibility anisotropies (in units of 10⁻⁶ erg/G²·mole) are $2_{\mathrm{\chi aa}}{\mathrm{\hspace{0.17em}-\hspace{0.17em}}}_{\mathrm{\chi bb}}{\mathrm{\hspace{0.17em}-\hspace{0.17em}}}_{\mathrm{\chi cc}}\text{\hspace{0.17em}=\hspace{0.17em}25.4\hspace{0.17em}±\hspace{0.17em}0.2}$ and $2_{\mathrm{\chi bb}}{\mathrm{\hspace{0.17em}-\hspace{0.17em}}}_{\mathrm{\chi aa}}{\mathrm{\hspace{0.17em}-\hspace{0.17em}}}_{\mathrm{\chi cc}}\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}4.1\hspace{0.17em}±\hspace{0.17em}0.15}$ . The molecular quadrupole moment obtained from this data (in units of 10⁻²⁶ esu·cm²) are $Q_{\mathrm{aa}}{\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}0.06\hspace{0.17em}±\hspace{0.17em}0.16, Q}}_{\mathrm{bb}}\text{\hspace{0.17em}=\hspace{0.17em}0.33\hspace{0.17em}±\hspace{0.17em}0.12}$ , and $Q_{\mathrm{cc}}\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}0.27\hspace{0.17em}±\hspace{0.17em}0.20}$ . The Stark effect produced by the motion of the molecules in the magnetic field $\mathrm{(ῡ\hspace{0.17em}\times \hspace{0.17em}B̄)}$ was clearly observed.