Fourier transform infrared spectroscopy of the ν₃ hot band of NO₃

We report the infrared spectrum of NO₃ studied with a high-resolution Fourier transform spectrometer. By improving the setup of an absorption cell, the following eight bands were observed at 1127, 1132, 1134, 1173, 1413, 1492, 1562, 1927 cm^-1 in the 1000-1930 cm^-1 region. The 1127, 1132, 1134, and 1562 bands were not reported previously by matrix isolation spectroscopy, and these bands have been assigned to hot bands from the ν₄ state (ν₃ + ν₄ ← ν₄) and (ν₃ + 2ν₄ ← ν₄). The analysis of the 1127 band with an E'-E' type spectral pattern has been carried out, and major molecular constants of the lower (ν₄) state are determined as follows: B = 0.459 2222(60), C = 0.227 8233(40), Cζ₄ = -0.042 063(15), and ν₄ = 365.48419(43) cm^-1. Two A'-E' type bands with band origin frequencies of 1132 and 1134 cm^-1 are also assigned, indicating that the 1492 band is assignable to ν₃ + ν₄, in contrast to the previous ν₃ assignment. A simultaneous analysis of the 1127, 1132, 1134, 1492 cm^-1 bands has been carried out to give 46 molecular constants for the ν₃ + ν₄ and ν₄ states. The molecular constants of the ν₃ + ν₄ A' states are different from those of the E' state, because of an effect of vibronic interaction from the B^2E′ electronic state to the ν₃ + ν₄ E' state.