Measurements of Deuterium Quadrupole Coupling in Formic Acid

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Abstract
The 101–000 rotational transition was observed in HCOOH, HCOOD, and DCOOH using a maser spectrometer. Quadrupole hyperfine structure was completely resolved in HCOOD and DCOOH. The measured quadrupole coupling strength along the OD-bond direction was eqQ = 391 kHz and HCOOD and eqQ = 249 kHz along the DC-bond direction in DCOOH. These coupling constants and the deuterium quadrupole coupling in NH2D are compared with the corresponding force constants and the results are in fairly good agreement with the theory of Salem.