Inversion frequencies of 15NH3 in the ground vibrational state are measured to an accuracy of ±0.01 MHz. The observed 115 lines, up to J = 18, including 54 new lines, are analyzed with 15-term Costain's exponential expression. The parameters reproduce the observed frequencies with a standard deviation of 0.053 MHz. Coupling constants of higher order vibration-rotation interaction for K = 3 and K = 6 levels are included in the analysis.
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