The ν2, 2 ν2, 3 ν2, ν4, and ν2 + ν4 bands of 15NH 3

The ir absorption of gaseous ¹⁵NH ₃ between 510 and 3040 cm ^-1 was recorded with a resolution of 0.06 cm ^-1. The ν₂, 2 ν₂, 3 ν₂, ν₄, and ν₂ + ν₄ bands were measured and analyzed on the basis of the vibration-rotation Hamiltonian developed by V. Špirko, J. M. R. Stone, and D. Papoušek ( J. Mol. Spectrosc.60, 159-178 (1976)). A set of effective molecular parameters for the ν₂ = 1, 2, 3 states was derived, which reproduced the transition frequencies within the accuracy of the experimental measurements. For ν₄ and ν₂ + ν₄ bands the standard deviation of the calculated spectrum is about four times larger than the measurements accuracy: a similar result was found for ν₄ in ¹⁴NH ₃ by Š. Urban et al. ( J. Mol. Spectrosc.79, 455-495 (1980)). This result suggests that the present treatment takes into account only the most significant part of the rovibration interaction in the doubly degenerate vibrational states of ammonia.