10min:
THE INVERSION SPLITTING OF 15NH2D AND 15ND2H AS OBTAINED FROM THEIR FIR SPECTRA.

M. ELKEURTI, Laboratoire d'Etudes Physico Chimiques, 20000 Sa\"\ida, Algérie; L. H. COUDERT, J. ORPHAL, LISA, CNRS/Universités Paris 12 et 7, 61 Avenue du Général de Gaulle, 94010 Créteil, France; C. E. FELLOWS, Laboratório de Espectroscopia e Laser, Universidade Federal Fluminense, Campus da Boa Viagem, Niterói, RJ, 24210-340, Brazil; AND S. TOUMI, Institut d'Electronique, Université Mokhtar Badji, 23000 Annaba, Algérie.

The far infrared absorption spectra of the partially deuterated species 15NH2D and 15ND2H have been recorded in the 20 to 105~cm-1 region using a Brucker IFS 120 Fourier transform spectrometer. A 25~cm long absorption cell with teflon windows was filled with different mixtures of 15NH3 and 15ND3 at total pressures ranging from 0.8 to 2 mbar. Several spectra with different 15NH2D to 15ND2H ratio were thus recorded. For all spectra the maximum path length was used resulting in a 2× 10-3~cm-1 resolution.

Prior to the line assignment, rotational constants for 15NH2D and 15ND2H where calculated from those of 14NH2D and 14ND2H. The IAM-type theoretical approach developed by Cohen and Pickett, which accounts for the large amplitude inversion motion and its coupling with the overall rotation, was afterwards used to obtain rovibrational energies and predicted spectra. In the case of 15NH2D, observed line positions for low- J lines were sometimes within 0.050~cm-1 from their predicted values.

The line position analyzes are still in progress. For both species, they are carried out with the help of the IAM-type theoretical approach.a For 15NH2D more than 300 a- and c-type lines have already been assigned and the observed wavenumbers are reproduced with an RMS deviation of 0.4× 10-3~cm-1. This will be discussed in the paper and the values obtained for the spectroscopic constants will be reported and compared to those obtained by Fusina et al. for the 14N-species. The decrease of the tunneling inversion splitting which goes from 0.406~cm-1 in 14NH2Db to 0.383~cm-1 in 15NH2D will also be discussed.