Molecular Rotational Spectra

Rotational spectra of diatomic molecules measured in the high-precision experiments are analyzed. Such a spectrum is usually fitted by an 8th order polynomial in spin. In fact, from the theoretical point of view, the rotational spectrum is expected to be a smooth function of spin. Thus, fitting the rotational spectrum in terms of a low order polynomial in spin seems to be justified. However, this is not what we found in the present work. We show that the measured spectrum is not necessarily a smooth function of the spin, which is quite surprising. Whether or not it indicates the presence of some hidden physics is an open question.