Improved ground state and [formula omitted] = 1 state rovibrational constants of 13C2D4

Abstract

The rovibrational spectrum of the ν12 band of isotopologue ethylene (13C2D4) was recorded using the Fourier transform infrared (FTIR) spectrometer with an unapodized resolution of 0.0019 cm−1 in the 1000–1140 cm−1 region. From the analysis of this A-type band, the v12 = 1 state rovibrational constants up to four quartic terms (ΔJ, ΔK, δJ, δK) were improved from previous work and a sextic term was derived for the first time. A total of 2403 infrared transitions were fitted using the Watson's A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.00026 cm−1. The band centre of the ν12 band of 13C2D4 was found to be 1069.969827(13) cm−1. The ground state rotational constants (B, and C) and the centrifugal distortion constants (ΔJ, δJ, δK) were improved with higher accuracy while a sextic term was obtained for the first time through the fitting of 1209 ground state combination differences (GSCDs) derived from the IR transitions of the ν12 band, together with 504 previously reported GSCDs of the ν9 band of 13C2D4. The root-mean-square (rms) deviation value of this fit was 0.00027 cm−1. The uncertainty of the measured infrared lines was estimated to be ±0.0003 cm−1. Additionally, equilibrium state rovibrational constants up to five quartic terms, and rotational constants of the ground and v12 = 1 state were derived from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVQZ basis set, for comparison with the experimental results. These calculated ground state rotational constants of 13C2D4 agreed well within 0.60% of those determined from the GSCD fit in this work. Rotational constants (A, B, and C) of the v12 = 1 state of 13C2D4 were also calculated using B3LYP/cc-pVQZ and MP2/cc-pVQZ levels with an agreement of 0.56% or less to those derived experimentally.