The Inversion Splitting of 15NH2D and 15ND2H as obtained from their

FIR Spectra

M. Elkeurti,1 L. H. Coudert,2 J. Orphal,2

C. E. Fellows,3 and S. Toumi4

1University of Saïda, Algeria2Lisa, University of Créteil, France3Universidade Federal Fluminense, Brazil4University of Annaba, Algeria

What do we know about14NH2D and 14ND2H ?

Their microwave spectra were first studied by De Lucia and Helminger1 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 14NH3, they display a large amplitude inversion.

0.405 cm1 for 14NH2DThe tunneling splitting is:

0.170 cm1 for 14ND2H

3. Fusina, Di Lonardo, Johns and Halonen, JMS 127, 240 (1988).

No investigations of the microwave or

FIR spectra of 15NH2D and 15ND2H

have been carried out.

The observed FIR spectrum

It was recorded with a Bruker IFS 120 Fouriertransform spectrometer.

A 25 cm long absorption cell was filled with a mixture of 15NH3 and 15ND3.

The maximum path length was 5 m, the resolution was 0.002 cm1.

15ND3 J = 6 5

15NH3 J = 3 2

15NH3 J = 3 2

NH2D and ND2H are very asymmetric

0.31 for NH2D

is: 0.14 for ND2H

Spectrum assignment

A, B, C, and F1 were obtained from the structure2 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).

Observed and predicted wavenumbers

For 15NH2D: 458 transitions have been assigned

For 15ND2H: 483 transitions have been assigned

The theoretical treatment

Unlike NH3, NH2D and ND2H display a strong rotational-tunneling interaction which is accounted for using Cohen and Picket1 IAM-like treatment.

•Two sets of rotational constants: Av, Bv, Cv, with v = 0 or 1.

•A coupling term in F(Jx Jz Jz Jx) between tunneling states.

1. E. A. Cohen and H. M. Pickett, JMS 93, 83 (1982).

Analysis results

For 15NH2D: 395 FIR and 57 MW transitions.

RMS is 0.24 × 103 cm1 and 0.204 MHz.

For 15ND2H: 323 FIR and 60 MW transitions.

RMS is 0.33 × 103 cm1 and 0.293 MHz.

The microwave transitions were measured in Lille University by G. Wlodarczak.

NH2D molecular constants in cm1

Inversion splitting comparison

0.793

0.0480.158

0.383

The molecule-fixed axis system

1. E. A. Cohen and H. M. Pickett, JMS 93, 83 (1982).

We use an IAM1 molecule-fixed axis system.

x

z C3

8°