Far-infrared laser stark spectroscopy of PH3

The laser Stark spectra of phosphine have been studied using the 195- and 195'-mu m lines of the DCN laser. The spectra were taken at room temperature for both parallel and perpendicular polarizations up to 57 000 V/cm. The observed resonances have been assigned to the pure rotational transitions J(K) = 6(K) <-- 5(K) in the nu(2) = 1 vibrational state for both E and A symmetries with K = 1 through 5. In addition, the zero-field forbidden transitions, J(K) = 6(3) <-- 5(3) A(1) <-- A(1) and A(2) <-- A(2), have been observed for the first time. The measured zero-field frequencies for all of the observed transitions are in excellent agreement with those calculated from the available molecular constants and represent an increase in accuracy over prior measurements. (C) 1997 Academic Press.