The \(Q\) -branch line of the fundamental transition of a diatomic molecule lies
at \(3142.3 \mathrm{cm}^{-1}\). The first line in the P-branch (that is, the
P-branch line closest to the Q-branch) is displaced in magnitude by \(21.2
\mathrm{cm}^{-1}\) from the Q-branch.
(a) Neglecting the effects of anharmonicity and centrifugal distortion,
compute \(v\) and \(\bar{B}\). Assume that the rotational constant is independent
of the vibrational level.
(b) Predict the wavenumber of the next P-branch line.
(c) Predict the wavenumber of the \(R\) -branch line closest to the Q-branch.
(d) If centrifugal distortion is considered, will the first \(\mathrm{P}\)
branch line be found at a higher, lower, or the same wavenumber as in part
(a)?