They are characterized by the rotational quantum number J = 0, 1, 2, 3, ... selection rules state that ΔJ is only able to take values of ± 1.:E(J) = h·B·J(J+1)The value of B is much smaller than ν e, such that a much smaller amount of energy is required to rotate the molecule; for a typical molecule, this lies within the microwave region.
Pri sobni temeraturi so skoraj vse molekule v osnovnem vibracijskem stanju v = 0.