Knowledge Bank

While $H3+$ does not possess a permanent electric dipole moment in its equilibrium position, the centrifugal distortion and the electrical and mechanical anharmonicity of the $molecule2$ produce a small dipole moment in the ground state, and in degenerate excited states, respectively. We have calculated the frequencies and intensities of rotational transitions induced by these dipole moments. Because of the small moments of inertia and the large vibrational amplitude in $H3+$, the induced transitions are much stronger than those of ordinary symmetric top $molecules3$. The effect of the forbidden transitions on thermalization of $H3+$ in space and possibility of detecting such transitions in the laboratory and in space will be discussed.