Determination of the electric dipole moment and excited state Fermi contact parameter of the GeCH radical

The germanium methylidyne (GeCH) radical has been studied at high resolutio n by laser-induced fluorescence spectroscopy in a skimmed molecular beam. T he radical was produced in a pulsed discharge jet source using methyltrichl orogermane as the precursor. Single rotational lines of the (A) over tilde (2)Sigma (+)-(X) over tilde (2)Pi (3/2) component of the 0(0)(0) band at 14 070 cm(-1) were recorded with linewidths of 35 MHz, showing resolved proto n magnetic hyperfine splittings. The observed hyperfine splittings of 12 ro tational lines were satisfactorily modeled by varying a single upper state Fermi contact parameter, giving b(F) = 163(2) MHz. Optical Stark measuremen ts were performed on the (GeCH)-Ge-74 P-11(3/2)F' = 1 hyperfine transition and the permanent electric dipole moments determined to be mu((X) over tild e (2)Pi) = 0.122(2) D and mu((A) over tilde (2)Sigma (+)) = 1.29(2) D. Our ab initio predictions of the dipole moments and excited state Fermi contact parameter are in fair agreement with experiment. The magnitudes of the det ermined parameters are discussed based on the molecular orbitals and compar ed to similar measurements on SiCH. (C) 2001 American Institute of Physics.