The analysis of the Coriolis interactions in the <i>v</i>₁₀ = 1, <i>v</i>₇ = 1 and <i>v</i>₄ = 1 triad rovibrational states of ¹³C₂D₄ by high-resolution FTIR spectroscopy

The high-resolution Fourier transform infrared spectra of the <i>B</i>-type ν10 and <i>C</i>-type ν7 bands of ¹³C₂D₄ were recorded for the first time at a resolution of 0.0019 cm⁻¹ in the 515–825 cm⁻¹ region. The v10=1, v7=1 and v4=1 states are coupled through <i>a</i>-, <i>b</i>- and <i>c</i>-axes Coriolis resonances. Local perturbations between v7=1 and v4=1 rendered some transitions in the infrared inactive ν4 band sufficiently intense for analysis. A total of 6379 infrared transitions (4684 of ν7, 1511 of ν10 and 184 of ν4) were assigned for the first time and fitted with an rms deviation of 0.00042 cm⁻¹, with a Hamiltonian containing Watson-type rotational terms in the Ir representation and <i>A</i>-reduction in the diagonal ν blocks and eight off-diagonal Coriolis terms to derive precise rovibrational constants for the upper states. Ground state spectroscopic constants up to sextic terms were also derived from a fit of 5266 ground state combination differences (GSCDs) with an rms deviation of 0.00045 cm⁻¹, from infrared transitions of the present analysis and those determined previously. The experimental constants of the ground and upper states compared favourably to the theoretically calculated constants using the cc-pVQZ basis set at MP2 and B3LYP levels.