THE SPECTRUM OF ROTATING WAVEPACKETS OF HINDERED METHYL-GROUPS

The wavefunction of a quantum system driven by a thermal environment localises when environmentally induced motion overtakes oscillations of the undriven system. The slowing down of the oscillations with increasing temperature is an important aspect of the transition from wave-like to particle-like behaviour. It is clearly displayed in the temperature-dependent motional spectrum of hindered methyl groups. Three resolved peaks at low temperature converge and broaden with increasing temperature. A one-parameter model of the transition extends the high-temperature hopping model into the quantum regime and agrees well with scattering measurements.