---
abstract: 'The fact, that $^4$He atoms on different concentric circular paths around the axis of a quantum vortex move with identically equal angular momentum, which represents an important aspect of superfluidity of He-II, has been used to discover a model which can explain the [*typical nature*]{} of experimentally observed $N$ (number of $^4He$ atoms) dependence of the rotational constant ($B$) of the rotor part of a cluster M:He$_N$. It reveals how exactly superfluidity is related to the said dependence of $B$ on $N$. We believe that this model, when used with simulation techniques, would render results that would agree closely with experiments.'
---

On the free rotation of a molecule embedded in helium-4 clusters

**Y. S. Jain$^1$ and S. Dey$^{1,2}$**

[**$^1$Department of Physics, North-Eastern Hill University, Shillong - 793022, India**]{}

[**$^2$Department of Basic Sciences, Assam Don-Bosco University, Guwahati - 781017, India**]{}

Key words : microscopic-superfluidity, He-clusters, He-nano-droplets.

PACS : 67.25. dw; 36.40.Mr; 36.40.-c

© by authors.

Ever since the spectroscopic study of SF$_6$ molecule embedded in superfluid helium-4 (He-II) was performed by Goyal [*et.al.*]{} [@goyal], rotational and vibrational dynamics of several molecules (say, OCS, CO$_2$, CO, N$_2$O, HCCCN, [*etc.*]{}, represented by M) embedded in bulk He-II and its nano-droplets 