Fourier transform infrared spectroscopy of the ν₂ and ν₄ bands of NO₃

High-resolution Fourier transform infrared spectra of the ν₂ and ν₄ bands of the ¹⁴N and ¹⁵N isotopic species of NO₃ were observed in the 762, 742, 365 and 360 cm ^-1 regions. ΔK = 3 combination differences of the ground state were obtained by using data of the ν₄ band combined with the ν₃ + ν₄ ← ν₄ band data in the 1127 cm^-1 region and the ν₃ + ν₄ band data in the 1492 cm^-1 region, and the C₀ constant was determined for the first time to be 0.2286274(57) cm^-1 and 0.2286547(58) cm^-1 for ¹⁴NO₃ and ¹⁵NO₃, respectively. The inertial defects derived from the observed B₀ and C₀ constants were in agreement with the calculated values obtained by using the Coriolis coupling constants ζ₄ = -0.188 for ¹⁴NO₃ and -0.156 for ¹⁵NO₃ obtained from the analysis of the data. The ν₂ band of ¹⁵NO₃ was observed for the first time in the 742 cm^-1 region. In contrast to the case of ¹⁴NO₃ reported by Friedl and Sander [J. Phys. Chem. 91 (1987) 2771], the effect of the perturbation from the 2ν₄ state was found to be small in ¹⁵NO₃. However, Coriolis and l-type resonance terms were essential to explain the observed anomalies, such as the staggering in the K′ = 3 levels. From an analysis including such interactions, the vibrational energies have been determined for the isomers to be, ν₂ = 762.3405(5), 2ν₄(l = 0) = 751.809(18), 2ν₄(l = 2) = 771.708(23) cm^-1 for ¹⁴NO ₃, and ν₂ = 742.7120(3), 2ν₄(l = 0) = 742.596(15), 2ν₄(l = 2) = 761.219(30) cm^-1 for ¹⁵NO₃. Crown