Infrared Diode Laser Spectroscopy of SiF and SiF

Author Institution: Department of Chemistry, Faculty of ScienceThe SiF radical was observed in the positive column of a glow discharge of SiF4 and Ar mixture. The SiF lines were discriminated from much stronger SiF2 lines by the discharge current modulation and Zeeman modulation techniques. Totally 209 lines belonging to the $^{2}\Pi_{1/2}$ and $^{2}\Pi_{3/2}$ spin states were identified for the fundamental band and hot bands up to $\nu 9 - 8$ in the ground electronic state. Most of the lines in the $^{2}\Pi_{1/2}$ state were observed with splitting due to the A-type doubling. The harmonic frequency obtained is $857.3251 \pm 0.0007 cm^{-1}$, where the uncertainty corresponds to three standard deviations. The equilibrium bond length $r_{g}$ is derived as $1.600 997 \pm 0.000 002$ from the rotational constant, $B_{r} 0.581 257 \pm 0.000 001 cm^{1}$. The SiF ion was observed in the hollow cathode discharge of pure $SiF_{4}$. Twenty one and ten lines in the R and P branches, respectively, of the fundamental band and some lines in the $\nu = 2 - 1$ hot band were recorded using the discharge modulation technique. A sharp decrease of the intensity caused by the magnetic field, which is characteristic to ion lines, was observed. From the band origins for the fundamental and hot bands, the harmonic frequency $\omega = 1050.3757 \pm 0.0013 cm^{-1}$ and the anharmonic constant $\omega x_{e} = 4.9462 \pm 0.0004 cm^{-1}$ are derived. The equilibrium bond length $r_{e} - 1.526 52 \pm 0.000 08$ derived from the rotational constant is considerably shorter than the value of the SiF radical