15min:

R. M. LEES, Department of Physical Sciences, University of New Brunswick, Saint John, NB, Canada E2L 4L5.

The infrared spectrum of the N-15 isotopic species of ammonia is being investigated in the 6370-6580 cm^-1 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 ₁ + ₃ N-H stretching combination band of normal ¹⁴NH₃, permitting immediate assignment by analogy with the known N-14 transitions. For ¹⁵NH₃, the ₁ + ₃ band origin is shifted downwards by 12.2 cm^-1 relative to ¹⁴NH₃. 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.