STUDY OF THE K = 3N A1-A2 CENTRIFUGAL SPLITTING IN THE 3-NU-2 AND 4-NU-2 STATES OF PH3 USING A DIFFERENCE-FREQUENCY LASER SYSTEM

A frequency tunable infrared source has been constructed by using the (Ar-laser) - (dyelaser) difference frequency method developed by Pine and applied to the observation of the overtone bands of PH3 3ν2 ← 0 and 4ν2 ← ν2 in the 3.4 μm region and 4ν2 ← 0 in the 1.6-μm region. A Stark modulation method was used to increase the sensitivity of detection. For transitions which were well modulated, the minimum detectable absorption coefficient was estimated to be ∼3 × 10-7 cm-1 using a 3-m cell. Emphasis was placed on the observation of the A1-A2 splitting for K = 3n rotational levels. For the 3ν2 state splittings were observed for K = 3, 6, and 9 because PH3 is a very nearly spherical top in this state. The magnitude and the J dependence of the observed K = 3n splittings have been analyzed by using a normal symmetric rotor Hamiltonian and a centrifugal distortion term of the form τxxxz[(J+3 + J-3)Jz + Jz(J+3 + J-3)] 4. © 1979.