High resolution near infrared spectrum of solid nitrogen, pure and doped with carbon dioxide Original Research Article

Near infrared spectra of solid nitrogen, pure or doped with carbon dioxide, natural or enriched in 13C, and also enriched with 15N2, were recorded at a high resolution with a Fourier transform spectrometer. The fine structure of the vibrational absorption of N2, 14N 15N and 15N2, induced by a Fermi resonance with the ν3 carbon dioxide vibrational mode, was analysed. The off-diagonal coefficients of the resonance and the relative zero order transition moments were evaluated for the complex CO2⋯N2, under the assumption of CO2 trapped in a monosubstituted site of S6 symmetry. The shifts from the gas phase values of the ν3 frequencies of the CO2 isotopes were fitted by a dispersion type curve with three frequencies of resonance, one corresponding to the phonon band around 2370 cm−1, one to the nitrogen induced absorption around 2328 cm−1 and one around 2298 cm−1 which does not correspond to any detectable absorption. We were unable to propose a convincing explanation for this last resonance.