31st Annual Meeting of the DPS, October 1999
Session 54. Outer Planet Physics II Posters
Poster Group II, Thursday-Friday, October 14, 1999, Kursaal Center

## [54.01] Collision-Induced Absorption Spectra of H2-H2 Pairs in the Second Overtone (3-0) Hydrogen Band at Temperatures 50 to 500~K: New Semi-empirical Model

A. Borysow (NBIfAFG/DK), J. Borysow (MTU/USA)

We have computed collision-induced rotovibrational~(RV CIA) absorption spectra in the near-infrared~(NIR) spectral range of hydrogen-hydrogen complex. The absorption by H2-H2 pairs in NIR is due to the second vibrational overtone and peaks at the wavelength region between 0.77 and 0.86~\mum. Both single~(H2(\Delta v=3)--H2(\Delta v=0) and double~ (H2(\Delta v=2)--H2(\Delta v=1) vibrational transitions are included in the calculations.

We have fitted the experimental data of the second overtone of H2--H2 by a series of simple analytical three parameter functions. The parameters were adjusted to represent closely within few percent (and experimental errors) the existing measurement at 77~K [1]. Thereafter, their temperature dependence was forced to follow closely the theoretical, quantum mechanical computations by Fu {\em et al.}~[2]. The model obtained in this way does represent the experimental data at 300~K also within few percent. This approach allows to obtain reliable RV CIA spectra of hydrogen pairs in (3-0) band at any temperature within a broad temperature range. The new model [3] assumes that both hydrogen molecules are initially in their ground vibrational states, therefore is suitable for low temperatures only, e.g. 50 to 500~K. It is especially valuable for studying the Uranus and Neptune atmospheres. The model can be used to calculate spectra for any ortho-to-para hydrogen ratio. {\sc Fortran} program is available at www.astro.ku.dk/~aborysow/programs/ and can be used freely provided reference to the original paper describing the method [3] is given.

The authors acknowledge support from NASA, Division for Planetary Atmospheres, Grant NAG5-4534. \\[3mm] 1. C.~Brodbeck, J.-P. Bouanich, Nguyen-Van-Thanh, Y.~Fu and A.~Borysow, {\em J. Chem. Phys.}, 110, 4750, (1999) \\ 2. Y.\ Fu, C.\ Zheng and A.\ Borysow, {\em JQSRT}, (1999), {\em in press} \\ 3. A.\ Borysow, J.\ Borysow and Y.\ Fu, {\em Icarus}, (1999), {\em submitted}