Assignment and modeling of 13CH4 spectrum at 298 K in the lower part of the Tetradecad in the 4970–5300 cm−1 range

Abstract

The absorption spectrum of the ¹³CH₄ methane isotopologue was recorded on a Bruker IFS-125HR Fourier transform spectrometer at 298 K in the 4970–6200 cm⁻¹ range. In this paper we report the results of assignment and modelling of the line positions and intensities of ¹³CH₄ in the range of weaker absorption between 4970 and 5300 cm⁻¹, corresponding to the lower part of Tetradecad, dominated by the 4ν₄ band system near 5180 cm⁻¹. The empirical list in this spectral range contains 1642 lines. Using an effective Hamiltonian initially derived from the analyses of cold Fourier transform (4970–5853 cm⁻¹) and laser direct absorption (5853–6200 cm⁻¹) spectra of the ¹³CH₄, we assigned 1600 lines belonging to four bands of the Tetradecad up to J_max=16. The 1548 line positions were fitted with an rms deviation of 1.7 × 10⁻³ cm⁻¹. Measured line intensities were modeled for 674 transitions using the effective dipole transition moments to an rms deviation of about 7 %. The new data were used for the simultaneous global fit of the ¹³CH₄ Hamiltonian parameters for the {Ground state / Dyad / Pentad / Octad / Tetradecad} system and the dipole moment parameters for the {Ground state - Tetradecad} system.