$N$ is increased from $N=N^i$ (the lowest $N$ for which experimental data are available) to certain $N = N^*$ that may depend on several factors like the size and symmetry of the structure of M, the strength of M-He interaction, [*etc*]{}.

\(B) It remains nearly constant when $N$ is increased beyond $N^*$ only by 1 or 2 or so but increases with further increase in $N$ up to another value, say $N_1$.

\(C) When $N$ is increased beyond $N_1$, $B$ is observed to decrease and increase alternately over different ranges of $N$, $N_1-N_2$, $N_2-N_3$, $N_3-N_4$, and $N_4-N_5$ and so on.

\(D) $\Delta\nu$ is observed first to increase linearly for first few $^4$He atoms (with $N < N^*$) but beyond this point it decreases with nearly a linear dependence on $N$; however, the slope of this decrease has different values over the ranges, $N^*-N_1$, $N_1-N_2$, $N_2-N_3$, $N_3-N_4$, and so on.

It is well known that $\Delta\nu$ is a simple consequence of a change in potential $V(Q_1, Q_2, ... ... Q_S)$ (governing all the $S$ possible vibrational modes of M) with changing $N$. It could be explained in terms of a small change in the related potential constant appearing in the harmonic 