Microwave spectroscopic detection of a transient phosphorus-bearing molecule, H3PO

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Abstract
The microwave spectrum of the transient phosphine oxide, H 3 PO , was detected in the gas phase for the first time using a source-modulated spectrometer. The H 3 PO molecule was generated in a free space cell by a dc glow discharge of a mixture of PH 3 , CO 2 , and H 2 gases and the corresponding spectral lines for each rotational transition of H 3 PO formed a pattern clearly indicative of a symmetric top molecule. Isotopomers of H 3 PO , i.e., H 3 P 18 O and D 3 PO were also produced; H 3 P 18 O in the same fashion as for H 3 PO , and D 3 PO , in a mixture of D 2 and CO 2 gases passing over red phosphorus grains. In total, 54 spectral lines of H 3 PO , 55 lines of H 3 P 18 O , and 61 lines of D 3 PO were measured for the fine structure of rotational transitions, J=2–1 to 12–11. The rotational constant, B 0 , and centrifugal constants, D J , D JK , and H KJ were ascertained by a least squares analysis of the measured frequencies for each of the species. Using the rotational constants of the three isotopic species, the following r 0 structure was determined: r 0 ( PO )=1.4763 Å, r 0 ( PH )=1.4406 Å, and ∠ HPO =114.26°. The value of each structural parameter deviates significantly from the most recent results predicted by ab initio calculations.

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