Experimental Determination of the Field Gradient at the Deuteron in Formaldehyde

A high-resolution microwave spectrograph has been constructed to observe small perturbations in rotational energy levels. High-resolution spectroscopy on OCD2 yielded the following values of the quadrupole coupling constants in the OCD2 principal inertial axis system: χaa = —13±4 kc/sec, χbb = 98±4 kc/sec, and χcc = —85±4 kc/sec. The spin—rotation coupling constants in OCD2 were calculated from the values for the proton obtained from the beam-maser spectroscopy on OCH2. Data on the 212→211 transition in OCHD is then analyzed yielding the following coupling constants in the OCHD principal inertial axis system: χa′a′ = 9±2 kc/sec, χb′b′ = 76±2 kc/sec, and χc′c′ = —85±2 kc/sec. The above data show that the principal field-gradient axis system coincides with the bond axis system within experimental error. The principal field-gradient components all in units of esu cm—3 are qαα (C–H bond axis) = 8.45×1014, qββ = —4.15×1014, and qγγ (perpendicular to molecular plane) = —4.30×1014.