文摘
The hyperfine coupling constants (hfcs) of two methyl radical isotopomers, CH2Mu and CD2Mu, have beenmeasured over a wide range of temperature in ketene and ketene-d2, from which the radicals were generated.The magnitudes of the hfcs of these muoniated methyl radical isotopomers are larger than those of CH3 andCD3 due to larger zero-point energy in the out-of-plane bending mode. In contrast to CH3 and CD3, where thecoupling constants become smaller with increasing temperature, the negative hfcs of the muoniated radicalswere found to increase in magnitude (become more negative) with temperature, passing through a maximumnear the boiling point of ketene. This behavior is attributed to a solvent-induced change in the force constantof the out-of-plane bending mode. The opposite temperature effect known for CH3 and CD3 is explained byexcitation of the low frequency out-of-plane bending mode. This effect is much smaller in the muoniatedradicals, where the vibrational frequency is significantly higher due to the light mass of muonium; consequently,the solvent effect dominates at low temperatures.