LABORATORY ROTATIONAL SPECTRUM OF PH (N=2[-1) IN THE 1 THZ REGION

The N = 2 <-- 1 rotational transition of the PH radical in its ground electronic (X(3)Sigma(-)) and vibrational states has been measured wit h the Cologne terahertz spectrometer in the frequency region between 9 20 and 1070 GHz. The PH radical was generated by immersing red phospho rus in a de glow discharge of molecular hydrogen buffered with argon. Transition frequencies of the five J' - J '' fine structure components together with the associated hyperfine structure patterns were precis ely measured and analyzed to derive highly accurate molecular paramete rs, which are more extensive than those reported in the existing liter ature. Among the determined parameters are the rotational constant B-0 = 252200.8099(63) MHz and the centrifugal distortion constant D-0 = 1 3.2915(33) MHz, as well as two fine structure constants - the spin-rot ation constant gamma(0) and the spin-spin interaction constant lambda( 0) - together with their centrifugal distortion contributions D-gamma 0 and D-lambda 0. Furthermore, each of the magnetic hyperfine paramete rs b(F), c, and the nuclear spin-rotation constants C-I were obtained for both nuclei. The accuracy of previously obtained molecular constan ts has been improved by up to one order of magnitude. This new set of molecular parameters allows highly reliable frequency predictions of t he rotational spectrum extending into the far infrared region; such tr ansition frequencies may be of interest for interstellar spectroscopy.