Matrix isolation spectroscopy in methane. Isotropic ESR spectrum of HC17O

The isotropic electron spin resonance (ESR) spectrum of HC17O has been observed in methane at 20 K (prepared by photolysis of HI in CH4 containing 1% of 17O enriched CO), and the isotropic oxygen hyperfine splitting determined [a0(HCO)=−15.1 G]. Isotropic spectra of HO2 (prepared similarly with O2 replacing CO) and NO2 in methane were also observed. Superhyperfine interactions in the ESR spectrum of H atoms in CH4 indicate H is trapped in the octahedral interstitial site of the matrix. ‘‘Forbidden’’ proton spin-flip transitions in the ESR spectrum of CH3 in methane indicate it is trapped at a substitutional site in the matrix.