Study on the high temperature line intensities of the symmetric-top molecule NH3

Abstract

The line intensities of 0300 a—0000 s transition of the symmetric-top NH3 molecule at high temperature were obtained by directly calculating the partition functions while regarding the rotationless transition dipole moment squared as a constant. The calculated values of the total internal partition sums (TIPS) are consistent with the data of HITRAN database within 0.19% at 296 K. The calculated line intensities data at 2000 K and 3000 K are also in excellent agreement with the data in HITRAN database with discrepancies less than -0.65% and -1.77%, which strongly supports the calculations of partition function and line intensity at high temperature. Then we extended the calculation to higher temperature. The line intensities and simulated spectra of 3ν2 band of the symmetric-top NH3 molecule at 4000 K and 5000 K were reported. The results are of significance for the study of the high-temperature molecular spectra in experiment and in theory.