Striking Anharmonic Resonances in N2O4: Supersonic Jet Fourier Transform Spectra at (13.3, 7.9, 5.7, and 3.2) Mu m

Published

February 1, 2000

Author(s)

M Hepp, R Georges, Martin Herman, J.- M. Flaud, Walter J. Lafferty

Abstract

The spectrum of N₂O₄ has been obtained in the (3.2, 5.7, 7.9, and 13.3) m regions, using a supersonic slit jet system coupled to a Fourier transform spectrometer with a spectral resolution of 0.005 cm^-1. Analysis of the spectra obtained indicates that the temperature of the molecular beam is close to 30 K. In the three lowest frequency spectral regions, not only were the upsilon_}9, υ₁₁ and υ₁₂ fundamental bands observed, but each fundamental was accompanied by an intense combination band which appears because of a strong anharmonic resonance leading to a transfer of intensity from the fundamental band to the combination band. In the 13.3 m region, two a-type bands with nearly equal intensities, are seen. Their band centers are υo(υ₁₂) = 747.85495(20) cm^-1 and υ_o(υ₆ + υ₁₀) = 755.37492(20) cm^-1. The 7.9 m region also contains two a-type bands whose band centers are υ_o(υ₁₁)=1261.08011(20) cm^-1 and υ_o(DB) = 1265.03219(20) cm^-1 where DB stands for dark band. This label is chosen because the assignment of the perturbing state can not be well established. In this region the combination band has about one third the intensity of the fundamental. In the 5.7 υm region, two b-type bands are observed with band centers υ_o(υ₉) = 1756.76217(20) cm^-1 and υ_o(υ₆ + υ₁₁) = 1733.15573(20) cm^-1 with the combination band having about a quarter of the intensity of the fundamental band. In addition, a much weaker combination band, υ₁ + υ₉, was observed in the 3.2 m region: υ_o(υ₁ + υ₉) = 3125.25987(30) cm^-1. All the bands were successfully analyzed leading to ground state combination differences which were combined with those obtained in a previous diode-laser study and fit to obtain ground state rotational constants. The upper state energy levels were fit using a Hamiltonian which explicitly takes into account the anharmonic resonances. The experimental data could be fitted to within their experimental uncertainties.

Citation

Journal of Molecular Structure

Volume

517

Pub Type

Journals

Keywords

anharmonic resonances, infrared spectrum, molecular beam supersonic jet spectra, nitrogen dioxide dimer

Citation

Hepp, M. , Georges, R. , Herman, M. , Flaud, J. and Lafferty, W. (2000), Striking Anharmonic Resonances in N₂O₄: Supersonic Jet Fourier Transform Spectra at (13.3, 7.9, 5.7, and 3.2) Mu m, Journal of Molecular Structure (Accessed April 25, 2024)