Infrared spectroscopy of difference and combination bands of the NO3 radical and anharmonicity analysis

The 2ν3-ν4 difference bands of 14NO3 and 15NO3 have been observed in the 1643.6 cm−1 and 1622.0 cm−1 region, respectively, and analyzed to determine molecular constants in the v3 = 2 state. The present paper also reports re-analysis of high-resolution spectra of the 15NO3 radical from 2000 to 2500 cm−1, which have been reported previously without vibrational assignments [J. Phys. Chem. A 114(2010), 980]. Three bands at 2004, 2128, and 2492 cm−1 are analyzed as the ν1 + ν3, 2ν3, and ν1 + ν3 + ν4 bands, including perturbations from nearby states. All vibrational states of 14NO3 and 15NO3 so far observed by infrared spectroscopy and laser induced fluorescence (LIF) are analyzed by using a vibrational energy matrix including cubic and quartic anhamonic effects, to determine anharmonicity constants and eigenvector coefficients. The first-order Coriolis coupling constants Cζ and the effective spin–orbit interaction constants aeff are calculated by using the eigenvector coefficients and compared with the observed values.