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

Abstract High-resolution Fourier transform infrared spectra of the ν 2 and ν 4 bands of the 14 N and 15 N isotopic species of NO 3 were observed in the 762, 742, 365 and 360 cm −1 regions. Δ K  = 3 combination differences of the ground state were obtained by using data of the ν 4 band combined with the ν 3  +  ν 4  ←  ν 4 band data in the 1127 cm −1 region and the ν 3  +  ν 4 band data in the 1492 cm −1 region, and the C 0 constant was determined for the first time to be 0.2286274(57) cm −1 and 0.2286547(58) cm −1 for 14 NO 3 and 15 NO 3 , respectively. The inertial defects derived from the observed B 0 and C 0 constants were in agreement with the calculated values obtained by using the Coriolis coupling constants ζ 4  = −0.188 for 14 NO 3 and −0.156 for 15 NO 3 obtained from the analysis of the data. The ν 2 band of 15 NO 3 was observed for the first time in the 742 cm −1 region. In contrast to the case of 14 NO 3 reported by Friedl and Sander [J. Phys. Chem. 91 (1987) 2771], the effect of the perturbation from the 2 ν 4 state was found to be small in 15 NO 3 . 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, ν 2  = 762.3405(5), 2 ν 4 ( l  = 0) = 751.809(18), 2 ν 4 ( l  = 2) = 771.708(23) cm −1 for 14 NO 3 , and ν 2  = 742.7120(3), 2 ν 4 ( l  = 0) = 742.596(15), 2 ν 4 ( l  = 2) = 761.219(30) cm −1 for 15 NO 3 .