Microwave spectrum of the PD2 radical in the 2B1 ground electronic state

The rotational spectrum of the PD2 radical in the 2B1 ground electronic state was observed in the region 165-463 GHz using a source-modulated microwave spectrometer. The PD2 radical was generated in a free-space absorption cell by a dc glow discharge of D2 over red phosphorus grains which were placed in the middle of the Pyrex glass cell. One hundred thirty fine and hyperfine components of 20 b-type rotational transitions were measured and analyzed by least-squares methods. The rotational and centrifugal distortion constants, the spin-rotation coupling constants with their centrifugal distortion terms, and the hyperfine coupling constants of both the phosphorus and the deuterium nuclei were precisely determined. The phosphorus nuclear spin-rotation coupling constants were found to have relatively large values: Caa(P) = 0.4815(89) MHz, Cbb(P) = 0.2501 (104) MHz, and Ccc(P) = 0.0564 (74) MHz, as suggested from those of PH2. The harmonic force field of PH2 was derived from centrifugal distortion constants, inertial defects, and the reported vibrational frequencies for PH2 and PD2. The determined force field was used to make harmonic corrections to the observed moments of inertia, and the rz structures for both species were derived, PH2: rz(PH) = 1.43365(23) A, θz(HPH) = 91.622(32)° and PD2: rz(PD) = 1.42852(17) A, θz(DPD) = 91.646(23)°, where errors in parentheses are due to residual inertial defects of the corrected moments of inertia. © 1998 Academic Press.