Comparative line position and line strength analysis of the v₂/v₄ dyad of ¹²CD₄ and ¹³CD₄

A highly accurate ro-vibrational analysis of FTIR spectra (line positions of (CD4)-C-13 and line strengths of both the (CD4)-C-12 and (CD4)-C-13 species) is presented. The high-resolution infrared spectra of both molecules were measured with a Bruker IFS125 HR Fourier transform infrared spectrometer at an optical resolution of 0.003 cm(-1) and analyzed in the regions of 800-1400 cm(-1) where the v(2)/v(4) dyad is located. The number of 901 transitions with J(max) = 23 were assigned to the v(4) and v(2) bands of (CD4)-C-13 (this number is about 5.3 times higher in comparison with the number of known assigned transitions for (CD4)-C-13). The weighted fit of experimental line positions was made using the Hamiltonian model which takes into account the resonance interactions between the (0001, F-2) and (0100, E) vibrational states. As a result, set of 18 fitted parameters of the (0001, F2)/(0100, E) vibrational states of (CD4)-C-13 was determined which reproduce the initial 901 experimental ro-vibrational line positions with the d(rms) = 2.59 x 10(-4) cm(-1), which is close to the experimental uncertainty of the recorded spectra and about 1330 times better in comparison with the reproduction of the same line position values by the use of parameters from Loete et al. (1983). The analysis of 1557 experimental lines of the dyad of (CD4)-C-12 and 131 lines of the dyad of (CD4)-C-13 was fulfilled with the Hartmann-Tran profile to simulate the measured line shape and to determine experimental line intensities. Sets of 6/1 varied effective dipole moment parameters of (CD4)-C-12/(CD4)-C-13 are determined which reproduce the initial 1557/131 line strengths with the d(rms) = 4.80% and 4.21%. Lists of the assigned line positions and strengths in the studied region are presented as the Supplementary data to this paper.