Atomic momentum distributions in polyatomic molecules in rotational-vibrational eigenstates

We report a quantum mechanical method for calculating the momentum distributions of constituent atoms of polyatomic molecules in rotational-vibrational eigenstates. Application of the present theory to triatomic molecules in the rovibrational ground state revealed that oscillatory changes appear on the proton momentum distribution in the nonlinear ${\mathrm{H}}_2\mathrm{O}$ molecule, whilst no such modulation is present in the case of an oxygen atom in the linear $\mathrm{C}{\mathrm{O}}_2$ molecule. The atomic momentum distributions were analyzed in detail by means of a rigid rotor model, and it was found that the oscillation originates from quantum-mechanical delocalization of the target atom with respect to the other atoms.