A new approach to the treatment of rotational spectra of molecules with small moments of inertia applied to the PH3 molecule in the ground state

A new approach to the treatment of rotational spectra of molecules with small moments of inertia is considered based on a representation of the effective rotational Hamiltonian operator in the form of a Pade operator. An extended set of high-precision data on transition frequencies in the rotational spectrum of the PH3 molecule in the ground vibrational state is analyzed. The fitting of these data within experimental error demonstrates the advantages of the new approach. Frequencies of the Q-branch forbidden transitions |K| = 3 ← 6, first measured in this work, represent an essential part of the data under consideration.