Hyperfine structure and the Stark effect in the electronic spectrum of theSiCH radical with implications for microwave spectroscopy and radioastronomy

A skimmed molecular beam of silicon methylidyne, SiCH, was produced using a pulsed discharge jet source with methyltrichlorosilane as the precursor. L inewidths of 35 MHz were achieved using laser-induced fluorescence detectio n. The field-free fine and magnetic hyperfine interactions and Stark effect s were analyzed for the (A) over tilde (2)Sigma (+)-(X) over tilde (2)Pi (3 /2) component of the 3(0)(1) band at 12 934.428 cm(-1). The observed proton hyperfine structure was satisfactorily reproduced with a single upper stat e Fermi contact parameter b(F)=117(2) MHz. The determined permanent electri c dipole moments are mu((A) over tilde (2)Sigma (+))=1.51(2) D and mu((X) o ver tilde (2)Pi (3/2))=0.066(2) D. Our ab initio predictions of the Fermi c ontact parameter and dipole moments at the B3LYP and quadratic configuratio n interaction including single and double substitutions levels of theory ar e in reasonable accord with experiment. An interpretation of the magnitudes of the determined parameters is given based on the highest occupied molecu lar orbitals. The very small ground state dipole moment will make microwave and radioastronomy studies of SiCH very challenging. (C) 2001 American Ins titute of Physics.