Knowledge Bank

The far infrared absorption spectra of the partially deuterated species $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$NH$2$D and $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$ND$2$H have been recorded in the 20 to 105 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ region using a Brucker IFS 120 Fourier transform spectrometer. A 25 cm long absorption cell with teflon windows was filled with different mixtures of $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$NH$3$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$ND$3$ at total pressures ranging from 0.8 to 2 mbar. Several spectra with different $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$NH$2$D to $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$ND$2$H ratio were thus recorded. For all spectra the maximum path length was used resulting in a $2\times 10-3$ cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ resolution. Prior to the line assignment, rotational constants for $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$NH$2$D and $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$ND$2$H where calculated from those of $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$NH$2$D and $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$ND$2$H. The IAM-type theoretical approach developed by Cohen and Pickett,} {\bf 93,} 83 (1982).} 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$NH$2$D, observed line positions for low-{\em J} lines were sometimes within 0.050 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ 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. For $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$NH$2$D more than 300 $a$- and $c$-type lines have already been assigned and the observed wavenumbers are reproduced with an RMS deviation of $0.4\times 10-3$ cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$. 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 {\em et al.}} {\bf 127,} 240 (1988).}\ for the $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$N-species. The decrease of the tunneling inversion splitting which goes from 0.406 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ in $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$NH$2$D to 0.383 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ in $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$NH$2$D will also be discussed.