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RESEARCH PRODUCT

High-Resolution Stimulated Raman Spectroscopy of Methane 13CD4 in the Pentad Region

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Abstract We present the first Raman spectrum of 13CD4 recorded at room temperature in the pentad region by inverse Raman spectroscopy, thus including the ν1 (A1), 2ν2 (A1), 2ν4 (A1), and ν2 + ν4(F1 + F2) Q branches. It is noteworthy that the overtone bands 2ν2 and 2ν4 are observed for the first time in a methane-like molecule by a coherent Raman process. The wide frequency range investigated, covering 45 cm−1 in three parts, contains more than 300 lines with uncertainty less than 10−3 cm−1 in most cases. These Raman data are combined with high-resolution infrared data in a weighted least-squares fit of the vibration-rotation constants of the pentad, thanks to a relevant partially reduced effective Hamiltonian including all the third-order interaction terms between the upper states of the five vibrational bands. These interactions within the pentad induce strong perturbations in the isotropic Raman spectrum. In particular the ν1 band exhibits a complex structure, which results essentially from the second-order Coriolis interaction between the v1 = 1 (A1) state and the v2 = v4 = 1 (F1) state. The analysis has been realized up to J = 18 in such a way that almost all of the Raman transitions were assigned up to J = 17. These observed Raman transitions are reproduced with an overall weighted standard deviation of 1.86 × 10−3 cm−1, which is the order of magnitude of the accuracy of the experimental data.