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

Abstract

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 360cm−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 1127cm−1 region and the ν3+ν4 band data in the 1492cm−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 742cm−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 14NO3, and ν2=742.7120(3), 2ν4(l=0)=742.596(15), 2ν4(l=2)=761.219(30)cm−1 for 15NO3.