Si2, SiH3, and HSiO molecules: ESR at 4 K

ESR spectra of 29Si2, 29SiH3, and H29SiO molecules in argon and/or neon matrices at 4 K have yielded the following new data: Si2 has a zero-field splitting in its ground3Σ−g state of ‖D‖=2.53(1) cm−1 in an argon matrix, which extrapolates to a gas-phase parameter of ‖λ‖=1.35(5) cm−1. The hyperfine interaction constant ‖A⊥(29Si)‖=40(2) MHz. SiH3 has g∥=2.0043(5), g⊥=2.0035(5), ‖Aiso(H)‖=25(3), ‖Aiso(29Si)‖=665(4), and ‖Adip(29Si)‖=166(3) MHz. Probable spin densities are 15% sSi+91% pSi−5% sH with a calculated bond angle of 113° in solid argon. HSiO has been observed for the first time. Its g components and spin distribution are very similar to those of the HCO radical. It is bent with a presumed 2A′ ground state, in accord with unpublished calculations of Bruna and Peyerimhoff and the recently published study of Frenking and Schaefer. The more stable isomer HOSi may have also been detected here.