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

Abstract

A skimmed molecular beam of silicon methylidyne, SiCH, was produced using a pulsed discharge jet source with methyltrichlorosilane as the precursor. Linewidths of 35 MHz were achieved using laser-induced fluorescence detection. The field-free fine and magnetic hyperfine interactions and Stark effects were analyzed for the à 2Σ+-X̃ 2Π3/2 component of the 301 band at 12 934.428 cm−1. The observed proton hyperfine structure was satisfactorily reproduced with a single upper state Fermi contact parameter bF=117(2) MHz. The determined permanent electric dipole moments are μ(à 2Σ+)=1.51(2) D and μ(X̃ 2Π3/2)=0.066(2) D. Our ab initio predictions of the Fermi contact parameter and dipole moments at the B3LYP and quadratic configuration interaction including single and double substitutions levels of theory are in reasonable accord with experiment. An interpretation of the magnitudes of the determined parameters is given based on the highest occupied molecular orbitals. The very small ground state dipole moment will make microwave and radioastronomy studies of SiCH very challenging.