Millimeter-wave spectroscopy of the SiCl+ ion

Abstract The millimeter-wave spectrum of the SiCl + ion in the ground and first excited vibrational states was observed for the two isotopic ( 35 Cl and 37 Cl) species. The ion was generated in a free-space absorption cell by a hollow cathode discharge of SiCl 4 diluted with He and discriminated from neutral species by the magnetic field effect on the absorption lines. The observed millimeter-wave spectrum was combined with a previously reported diode laser spectrum in an analysis to determine mass-independent Dunham coefficients as well as the mass scaling parameters. The equilibrium bond length of SiCl + determined is r e  = 1.943 978(2) A.