Knowledge Bank

The rotationally resolved spectra of the $\nu 3$ vibrational mode of $(CH4)n(n=1-2\times 103)$ clusters in He droplets have been measured. With increasing of the cluster size the effective rotational constant of the $CH4$ molecules in the cluster decreases and for $n>500$ the rotational structure collapses. This behavior suggests gradual quenching of the internal rotation of the $CH4$ molecules upon increase of the cluster size.