Coriolis interaction of the ν12 and 2ν10 bands of ethylene-cis-1,2-d2 (cis-C2H2D2) by high-resolution FTIR spectroscopy

Abstract

The spectrum of the A-type ν12 band of ethylene-cis-1,2-d2 (cis-C2H2D2) was recorded at an unapodized resolution of 0.0063cm−1 in the wavenumber range of 1270–1410cm−1. The band is perturbed through a c-type Coriolis resonance with the unobserved B-type 2ν10 band which is situated approximately 11cm−1 below the ν12 band center. In this work, a total of 73 new infrared transitions of high J and Ka values of the ν12 band were identified and assigned for a rovibrational analysis. Finally, a total of 844 perturbed and unperturbed infrared transitions (including those previously reported) of ν12 were assigned and fitted using Watson’s A-reduced Hamiltonian in the Ir representation with the inclusion of a second-order c-type Coriolis interaction term to derive a set of rovibrational constants of better accuracy for the ν12=1 state up to two sextic terms. Improved rotational and two quartic centrifugal distortion constants were also derived for the ν10=2 state of cis-C2H2D2 from the analysis of the Coriolis interaction between the two perturbing bands. The ν12 band is found to be centered at 1341.150877±0.000088cm−1 while that of 2ν10 is 1330.6360±0.0113cm−1. By fitting the infrared lines of ν12 with an rms deviation of 0.00067cm−1, a second-order c-Coriolis coupling constant was accurately determined. A set of ground state rovibrational constants up to two sextic terms of comparable accuracy to those previously reported was also derived from a simultaneous fit of a total of 1728 ground state combination differences (GSCDs) from the infrared transitions of the present analysis and those of the ν7 band of cis-C2H2D2 together with 22 microwave transitions. The root-mean-square deviation of the GSCD fit was 0.00030cm−1.