First high resolution study of the interacting v(8) + v(10), v(6) + v(10), v(6) + v(7) bands and re-analysis of the v(7) + v(8) band of trans-d(2)-ethylene

The high resolution IR spectrum of the trans-d₂-ethylene (trans-C₂H₂D₂) was recorded and analyzed in the region of 1450–1750 cm⁻¹, where the strongly interacting bands ν₈+ν₁₀, ν₇+ν₈, ν₆+ν₁₀, and ν₆+ν₇ are located (one of the sub-bands of the hybrid ν₇+ν₈ band was analyzed earlier; transitions belonging to the three other bands were experimentally recorded and assigned in the present study for the first time). For description of the upper ro-vibrational energy levels obtained from the assigned transitions, the used Hamiltonian takes into account resonance interactions both between four studied vibrational states, (v₈=v₁₀=1), (v₇=v₈=1), (v₆=v₁₀=1), (v₆=v₇=1), and between the state (v₆=v₇=1) and the additional fifth state (v₄=v₈=1) which is considered in the present study as a “dark” state. About 2360, 2150, 2020 and 1700 transitions with the values J^max./K_a^max.=31/21, 44/18, 28/18 and 27/17 were assigned to the bands ν₈+ν₁₀, ν₇+ν₈, ν₆+ν₁₀, and ν₆+ν₇, respectively. A set of 103 spectroscopic parameters was obtained from a weighted least square fit procedure. This reproduces the 550, 656, 441 and 435 upper ro-vibrational energies of the vibrational states (v₈=v₁₀=1), (v₇=v₈=1), (v₆=v₁₀=1) and (v₆=v₇=1) used in the fit with a d_rms=2.5×10⁻⁴cm⁻¹, which is close to the value of the mean experimental uncertainty (in this case, only upper energies obtained from unblended and nonsaturated transitions of relatively high intensities have been taken into account).