The transient thiophosphenous fluoride FPS was produced by pyrolysis of 2.5% F 2 PSPF 2 in Ar at 1300-1800 • C. Highresolution (≥0.004 cm -1 ) Fourier transform infrared spectra of the a-type ν 1 and b-type ν 2 bands, centered respectively at 803.249 and 726.268 cm -1 , were measured and fitted to rotational and quartic centrifugal distortion parameters. The millimeterwave spectrum, essentially b-type, was measured between 300 and 370 GHz in the ground state and in the ν 3 excited state for FP 32 S and in the ground state for FP 34 S. The frequencies were fitted to a Watson-type A-reduced Hamiltonian up to sextic distortion terms. High level ab initio calculations with large basis sets were performed on FPS and supported the first identification of its infrared and millimeter wave spectra. The calculated anharmonic force field provided precise ab initio rovibrational α constants which were combined with the experimental molecular parameters to determine an accurate equilibrium structure of the molecule: r e (PS) = 188.86 pm, r e (PF) = 158.70 pm, θ(FPS) = 109.28 • . The collision-controlled 1/e lifetime measured in a 10-Pa (1 : 20) F 2 PSPF 2 /Ar mixture was 2 s, more than two orders of magnitude larger than that of FPO under the same experimental conditions.