Knowledge Bank

The infrared spectrum of the N-15 isotopic species of ammonia is being investigated in the 6370-6580 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ region with an external cavity tunable diode laser spectrometer. The patterns of some of the stronger absorption lines are very similar to those known for the $\nu 1+\nu 3$ N-H stretching combination band of normal $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$NH$3$, permitting immediate assignment by analogy with the known N-14 transitions. For $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$NH$3$, the $\nu 1+\nu 3$ band origin is shifted downwards by 12.2 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ relative to $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$NH$3$. From the preliminary spectra, the absorption intensities appear fairly comparable for both species, but more careful measurements to better define the isotopic intensity ratio are underway.