Knowledge Bank

A technique employed earlier to calculate the rotational constants of $CH1OCH$ is extended to the ground and two vibrational levels in the $v1$ vibration of $CH1CN$ for several isotopic species. The moments of inertia and a computer iteration technique over experimental data for each isotopic species were employed to evaluate the constant $A1$ in an excited vibrational state for a symmetric top molecule. Several frames of reference were chosen and the vibrational configuration analyzed for each coordinate set. The angel of bending and the orientation of each molecular system in a reference frame fixed on the carbon atom at the û$C\equiv$N site were explore. The method, which was applied by Tam and Roberts to the nv, n=1, 2, 3, 4 vibrations of $CH3OCH$ earlier and which was extended to the $v10=1$ vibration of $CH3OCH$ with isotopic species, has been applied to $\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}C$ isotopic species of $CH3CN$ and seems to be a useful tool to extract the value of $Ac$. Values of $Ac$ over several vibrational levels have been calculated with different coordinate sets to establish a pattern for the HCH over vibrational levels. Values of A calculated from the geometrical model are in good agreement with those obtained by fitting the terms in the frequency equations, which contained A, to the experimental data through an iteration technique in which the value of A was allowed to vary. The values of A are compared to other published values.