First investigation of the ν1, ν1-ν9, ν1+ν9, and ν1+ν7 absorption bands of nitric acid (1H14N16O3) at 3551.766 cm−1, 3092.708 cm−1, 4006.974 cm−1, and 4127.782 cm−1, respectively

Abstract

This paper is the first of two back-to-back articles describing the first high resolution study and analysis of the rovibrational structure of the (mainly) A-type ν1 band, the (mainly) B-type ν1+ν7 band, and of the C-type ν1-ν9 and ν1+ν9 bands of nitric acid (H14N16O3) centered at 3551.766 cm−1, 4127.782 cm−1, 3092.708 cm−1, and 4006.974 cm−1, respectively. For this, high resolution Fourier transform laboratory spectra in the 2.8 µm, 2.4 µm, 3.2 µm, and 2.5 µm spectral regions were recorded at the SOLEIL synchrotron. The ν1 band is highly congested and perturbed and the identifications were often uncertain because of line overlap, due to the large value of the Doppler linewidths (∼0.003 cm−1 HWHM at 296 K). However, combining the analysis of the ν1 band with that of the ν1-ν9 difference band (centered at 3092.708 cm−1) proved to be highly helpful. Surprisingly enough, it appeared that the 11 energy levels are affected by torsional splitting, probably due to anharmonic resonances coupling together the 11 levels with those of vibrational states involving high excitation in the ν9 mode. Using an effective approach, we have generated a list of positions and intensities for the ν1 band and for the ν1+ν9-ν9 and ν1+ν7-ν7 hot bands in the 2.8 µm region.