Rotation of O_2 molecules in solid D_2 and HD: An electron spin resonance study

摘要

X-band electron spin resonance (ESR) spectroscopy has been applied to the study of molecular rotation of O_2 molecules in isotopic solid hydrogen, D_2 and HD. ESR signal of the O_2 molecules inhindered rotational states has been observed, and its pressure dependence has been measured up to 19 MPa. Although molar volume of solid hydrogen decreases, the O_2 rotation has become less hindered with the increase in pressure and isotope substitution from HD to D_2. These effects of pressure and isotope substitution suggest that the potential barrier for the O_2 rotation is mainly produced by distortion of O_2 cages I nD_2 and HD. Since solid hydrogen becomes less compressible with the increase in pressure and the isotope substitution from HD to D_2, the O_2 rotation becomes less hindered in the less distorted O_2 cages.