Submillimeter-wave spectra of the PH and PD radicals in the 3Σ - state

The lowest rotational spectral lines of the PH and PD radicals in their X ³Σ ^- ground vibronic state were observed by submillimeter-wave spectroscopy using a source-modulated system combined with a glow discharge free-space cell. The PH or PD radical was generated by the reaction of red phosphorus with dc glow discharged H ₂ or D ₂ gas. Twenty fine and hyperfine components of the N=1-0 transition of PH were measured in the frequency region of 423 to 553 GHz, and 50 components of the N=1-0 and 2-1 transitions of PD in the region of 181 to 523 GHz. The molecular constants, including the rotational constants, the spin—spin coupling constants with their centrifugal distortion terms, and the hyperfine coupling constants associated with the phosphorus, hydrogen and deuterium nuclei, were precisely determined by least-squares fitting to the observed spectral lines.