LINE-INTENSITIES IN THE FAR-INFRARED SPECTRUM OF H2O2

Using high resolution Fourier transform spectra (resolution 0.002 cm(- 1)) recorded at the Institute Ricerca Onde Electromagnetiche Firenze a nd at the Justus Liebig University Giessen, it has been possible to me asure the relative intensities of lines in the far-infrared spectrum o f H2O2 in the 25-400 cm(-1) spectral region. These intensities were us ed as input data in a least-squares fit calculation in order to obtain the expansion parameters of the transition moment operator of the pur e torsional-rotational transitions of H2O2. For these intensity calcul ations, the theoretical model takes into account the cos gamma-type de pendence of the dipole moment due to the large amplitude motion of the H atoms relative to the O-O bond, where 2 gamma is the torsion angle. The value of the dipole moment obtained from the fit of the observed intensities was then scaled to the value obtained from Stark effect me asurements. Finally, a synthetic spectrum of the far infrared band of H2O2 was generated, using the dipole moment expansion determined in th is work for the line intensities and the parameters and the Hamiltonia n matrix given in a previous analysis (C. Camy-Peyret, J.-M. Flaud, J. W. C. Johns, and M. Noel, J. Mel. Spectrosc. 155, 84-104 (1992)) for the line positions. In addition to the (Delta n = +/-1, Delta K-a = -/ +2) torsional-rotational resonances within the ground vibrational stat e, which are usually observed for H2O2, the Hamiltonian model takes ex plicitly into account both the vibration-rotation resonances involving the ground state and the upsilon(3) = 1 vibrational state and the ''s taggering'' effect which is due to the cis potential barrier. (C) 1996 Academic Press, Inc.