Velocity modulation infrared laser spectroscopy of negative ions: The (011)-(001) band of azide (N₃^-)

We have measured 43 transitions centered at 1972 cm^-1 in the (011)-(001 ) bending hot band of the azide ion (N₃^- ) using diode laser velocity modulation spectroscopy of an NH₃/N ₂O discharge. The data, ranging from P(32) to R(40), were fit to a standard ι-type doubling Hamiltonian through quartic terms. The ι splittings in the spectrum were unusually large compared with similar molecules. Intensity measurements indicate that the vibrational and rotational degrees of freedom are equilibrated, unlike the case for isoelectronic NCO^-. Additional lines of the ν₃ fundamental have also been measured, which further refine the values of the ground state parameters.