15min:

MIKHAIL N. SLIPCHENKO, HIROMICHI HOSHINA, ANDREY F. VILESOV, Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA.

The rotationally resolved spectra of the ₃ vibrational mode of (CH₄)_\mathrmn (\mathrmn = 1 - 2×10³) 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.