FTIR Spectroscopy of NO3: Perturbation Analysis of the ν3+ν4 State

High-resolution Fourier transform infrared spectra of the 15NO3 ν3+ν4 and ν3+ν4–ν4 bands were observed in the 1472 and 1112 cm–1 regions. Compared with the case of 14N species, large effects of perturbations were recognized in many rotational levels of the 15NO3 ν3+ν4 state, and it was found that the ν2+2ν4 state is responsible for the perturbation. Although a direct Coriolis interaction (Δν2 = 1, Δν3(or Δν4)=1) is not present between these two vibrational levels, anharmonic terms including Φ344 and Φ444 mix ν3+ν4 and 3ν4, ν2+2ν4, and ν2+2ν4 mixes with ν2+ν4 to produce Coriolis interaction between ν3+ν4 and ν2+2ν4. An analysis gave the energy difference of 7.274 cm–1 between two levels, and interaction parameters were determined. Similar perturbation analysis was applied for the 14N species, and the previous pP­(N,K) assignment of the ν3+ν4 A′-ν4 E′ band was changed for giving one A2′ state. Spectral lines to another A1′ state were not assigned because of weak intensity, which is explained by intensity anomaly through vibronic interaction, reflecting the transition moment of the B̃2E′–X̃2A2′ electronic band.