THE PURE ROTATIONAL SPECTRUM OF THE SiP RADICAL (X2Πi)

The millimeter-wave spectrum of the SiP radical in its X$^{2}$$\Pi$$_{i}$ ground electronic state has been recorded using direct absorption spectroscopy in the frequency range 151 – 532 GHz. The species was synthesized in an AC discharge by the reaction of SiH$_{4}$ and red phosphorous, in argon carrier gas. Both lambda-doubling and hyperfine splittings, from the phosphorus nuclear spin (\textit{I} = 1/2), were observed in both spin-orbit ladders, $\Omega$ = 3/2 and 1/2. The $\Omega$ =1/2 ladder appears to be perturbed, presumably by the nearby A$^{2}$$\Sigma$ state, as suggested by previous optical data. The data were analyzed with a Hund’s case (a) Hamiltonian, establishing global spectroscopic constants. A deperturbation analysis was also conducted, further refining the $\Pi$-$\Sigma$ interaction