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.