1. The Inversion Splitting of 15 NH 2 D and 15 ND 2 H as obtained from their FIR Spectra M. Elkeurti, 1 L. H. Coudert, 2 J. Orphal, 2 C. E. Fellows, 3 and S. Toumi 4 1 University of Saïda, Algeria 2 Lisa, University of Créteil, France 3 Universidade Federal Fluminense, Brazil 4 University of Annaba, Algeria

2. What do we know about 14 NH 2 D and 14 ND 2 H ? Their microwave spectra were first studied by De Lucia and Helminger 1 and then by Cohen and Pickett. 2 1. F. C. De Lucia and P. Helminger, JMS 54, 200 (1975). 2. E. A. Cohen and H. M. Pickett, JMS 93, 83 (1982). Their FIR spectra were investigated by Fusina et al. 3 Just like 14 NH 3, they display a large amplitude inversion. 0.405 cm  1 for 14 NH 2 D The tunneling splitting is: 0.170 cm  1 for 14 ND 2 H 3. Fusina, Di Lonardo, Johns and Halonen, JMS 127, 240 (1988). No investigations of the microwave or FIR spectra of 15 NH 2 D and 15 ND 2 H have been carried out.

3. The observed FIR spectrum It was recorded with a Bruker IFS 120 Fourier transform spectrometer. A 25 cm long absorption cell was filled with a mixture of 15 NH 3 and 15 ND 3. The maximum path length was 5 m, the resolution was 0.002 cm  1.

4. 15 ND 3 J = 6  5 15 NH 3 J = 3  2 NH 2 D and ND 2 H are very asymmetric  0.31 for NH 2 D  is:  0.14 for ND 2 H

5. Spectrum assignment A, B, C, and F 1 were obtained from the structure 2 and wavenumbers were calculated. 1. E. A. Cohen and H. M. Pickett, JMS 93, 83 (1982). 2. V. Danielis, D. Papousek, V. Spirko, and M. Horak, JMS 54, 339 (1975).

6. Observed and predicted wavenumbers For 15 NH 2 D: 458 transitions have been assigned For 15 ND 2 H: 483 transitions have been assigned

7. The theoretical treatment Unlike NH 3, NH 2 D and ND 2 H display a strong rotational- tunneling interaction which is accounted for using Cohen and Picket 1 IAM-like treatment. Two sets of rotational constants: A v, B v, C v, with v = 0 or 1. A coupling term in F(J x J z  J z J x ) between tunneling states. 1. E. A. Cohen and H. M. Pickett, JMS 93, 83 (1982).

8. Analysis results For 15 NH 2 D: 395 FIR and 57 MW transitions. RMS is 0.24 × 10  3 cm  1 and 0.204 MHz. For 15 ND 2 H: 323 FIR and 60 MW transitions. RMS is 0.33 × 10  3 cm  1 and 0.293 MHz. The microwave transitions were measured in Lille University by G. Wlodarczak.

9. NH 2 D molecular constants in cm  1

10. Inversion splitting comparison 0.793 0.048 0.158 0.383

12. The molecule-fixed axis system 1. E. A. Cohen and H. M. Pickett, JMS 93, 83 (1982). We use an IAM 1 molecule-fixed axis system. x z C3C3   8°