Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

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



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


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 υo6 + υ10) = 755.37492(20) cm-1. The 7.9 m region also contains two a-type bands whose band centers are υo11)=1261.08011(20) cm-1 and υo(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 υo9) = 1756.76217(20) cm-1 and υo6 + 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: υo1 + 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.
Journal of Molecular Structure


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


Hepp, M. , Georges, R. , Herman, M. , Flaud, J. and Lafferty, W. (2000), Striking Anharmonic Resonances in N<sub>2</sub>O<sub>4</sub>: Supersonic Jet Fourier Transform Spectra at (13.3, 7.9, 5.7, and 3.2) Mu m, Journal of Molecular Structure (Accessed June 15, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created January 31, 2000, Updated October 12, 2021