High-resolution FTIR spectroscopy of 12C2HD3 in the 830–1110 cm−1 region: A study of the Coriolis and anharmonic interactions within the v3 = 1, v6 = 1 and v8 = 1 triad

Abstract

The infrared spectrum of ethylene-d3 (12C2HD3) was measured between 830 and 1110 cm-1, covering the ν3, ν6 and ν8 bands, using a Fourier transform infrared (FTIR) spectrometer at an unapodized resolution of 0.0019 cm−1. The three upper vibrational states were found to mutually-interact through Coriolis and anharmonic resonances. A total of 2128 a- and b-type absorption lines of the ν3 band and 3107c-type lines of the ν8 band were assigned in this work. Although the ν6 band is relatively weak, 246 spectral lines were identified and included in the final fit for the rovibrational parameters of the upper vibrational states. Using a Hermitian Hamiltonian comprising Watson's-type rotational operators and off-diagonal interaction terms, three sets of rovibrational constants up to quartic terms were derived for the v3 = 1, v6 = 1 and v8 = 1 states together with thirteen interaction parameters, with a root-mean-square (rms) deviation of the fit = 0.00059 cm−1. The band centres of the ν3, ν6 and ν8 bands were determined to be 1044.260675 ± 0.000025 cm−1, 998.60182 ± 0.00060 cm−1 and 918.732573 ± 0.000019 cm−1 respectively. A set of ground state rovibrational constants of 12C2HD3 up to five quartic constants was also derived with improved precision from a simultaneous fit of 782 ground state combination differences (GSCDs) from a-type infrared transitions of the ν3 band and 1422 GSCDs from the c-type ν8 band from the present analysis, together with 377 GSCDs from the previous work on the 2ν8 band. The rms deviation of the GSCD fit was 0.00039 cm-1. The experimental spectroscopic parameters compare favourably with the quantum-chemically calculated values at the MP2/cc-pVQZ and B3LYP/cc-pVQZ levels of theory.