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 Jmax=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.