Rovibrational intensities in the ν4 band of ammonia

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Absolute line intensities of sixteen rovibrational transitions in the ν4 band of 14NH3 were measured around 1800cm−1 using a tunable diode laser spectrometer with a sweep modulation of the laser frequency. Individual laser scans over the line region were recorded to disk storage separately and the spectrum accumulation was performed off-line using a computer to reduce a significant line broadening because of a lower accuracy of the hardware on-line accumulation.From integrated absorption coefficients obtained by the numerical analysis of the measured line profile, the effective transition moments of individual rovibrational lines were derived. Using the second order perturbation theory of the transition moment of rovibrational transitions of the symmetric top molecules, the effective vibrational transition moments for the ν4 fundamental band of 14NH3 were estimated.